What I would do in terms of the roster

Lobbers- 2 plants
Cabbage pult- leafy lobbing leaves lasting lashes on lingering lifeforms foreign to the lawn.  Not much to say here other than it can hit flying enemies.
Seed spitter- seed spitter has three distinct traits- lobbing, area limited multihit, and being a fruit. Many fruit plants have area limited multihit, like melon pult with a 3x3 area of effect, akee being able to hit multiple zombies in its own lane, ghost pepper (which are fruits apparently) have a 1x3 attack range before exploding, bombegranite, pepper pult, solar tomato, theres a lot of limited area multihit fruits (I want to call it that so it can fit the likes of aoe like melon pult and contained bouncing like akee, and if you want to you can consider starfruit and dragon bruit although those just have multiple projectiles). Seed spitter itself would spit a hard seed, allowing it to bounce to another zombie in the same lane. I think the pure tier 3 would be akee, but im not sure what the tier 2 would be. I could also see akee being the tier 2, with apple mortar being a tier 3.

Support- 5 plants
Tangle Kelp- A very versatile plant, it stuns on land and deals great damage in the water. I wish this was more reflected in plants like zapture though. I also wish more biomes had water to begin with, like at least sewers. Leaky pipes would be a fun obstacle to temporarily change up the battlefield to power up your amphibious plants.
Wall Nut- I like wall nut a lot, I really do. I just think he charges too quick. I think walls are important and im glad he costs more now, providing support without directly affecting zombies really makes the game a lot more enjoyable since you can do things that arent just obliterate everything on sight, and its actually strategy instead of just min-maxxing. Strategic depth is very important Thats really all I have to say about him. Maybe he could make kiwi beast, using something like phat beats, maybe incorporating lychee too if it would be a tier 3?
Blover- Since instant use plants are basically off the table, I think blover could be a staller. Periodically pushing back zombies, especially fliers, is a fun niche I think. It would combo well with other stalling tools like chill, and increase the potency of plants like spikeweed. I don't want to add plantern, at least as a tier 1, because I cant think of a mechanic for its evolutions. Ill mention it here- maybe if plantern is a tier 2 we could get disco plants like disco chomper or a disco ball citron, since plantern both has glass and makes light. I do think I want to come up with some sort of glass plant though, since magnifying grass exists. One thing I do wish though is maybe that blovers could push ambushes/drops forward, like the meteors in the volcanos, so they are less likely to hit plants or take up important backline areas, alongside other future airborne threats.
Umbrella Leaf- I never would have thought about a counter attack mechanic- its brilliant and fun and makes umbrella leaf fusions fun. I just think there isnt enough triggers for it. Blocking attacks is really cool. Honestly this is probably the number one plant that makes me want to argue for 5 seed slots, maybe 6- I just think support plants like umbrella leaf deserve to be taxing on your seed slots. Of course you can neglect to bring it and replace your plants- so its not a necessity ever, especially if we get something like hot potato to break up those saganaki mounds. Maybe in the sewers we could get zombie goldfish that rain from the sky, since people often flush zombie goldfish down the toilet. I think umbrella leaf could deflect them.
Grave Buster- Grave buster could deal significant damage over time to graves instead of just destroying them in a set time. This allows it to exist long enough to evolve which I think is fun. Also- its a vine, at least in pvz2, so I want to dual purpose this plant- planting it on a plant provides a thorny vine, akin to pumpkin, which can be evolved to create the vines from pvz2 (or at least some). I think a design like this helps players choose different plants, since you would only evolve one plant at a time- if they want the vines, they have to put plants in them that dont evolve with the same plants the vine does. This isnt even too limiting to the player since they can just wait for the cooldown, but it still provides thoughtful gameplay that might encourage players to switch up what they use from time to time, if they really want to. In a game about making choices matter I think a plant like this is engaging and thought provoking without requiring a challenge. Its also just nice to have ambiguous plants (like tangle kelp being plantable on land) to allow players to use familiar plants and unlocked merges in levels without the plant's main function.

Gonna cover some elemental plants here- gonna try to do one permanent attacker and one "instant use" plant
Electric- 2 plants
Zaptail- I still think they should be amphibious. They're reeds. Reeds grow in the water! Other than that I think its cool. Zapture is goofy though I already suggested a rework in another thread. 
E.M.P.each- I might have mentioned it in the robots/elements rework forum? E.M.Peach is a charge plant that unleashes a large burst of electric damage when a zombie approaches it. The more charge levels it has the bigger the area and the higher the damage. E.M.Peach serves to stun mechs using the electrical system, and is fully charged when planted. This hopefully emulates its ability from pvz2 while providing diverse usage for it and not making it an instant use. To avoid players emptying the charge and evolving just to get full charge on a higher tier plant, E.M.Peach and its evolutions can only evolve while fully charged. EMPeach (for short, I guess) can evolve into plants like citron.
Cold- 2 plants
Snowdrop- I want to get this plant in as a tier 1, since we know this game and heroes take place around the same time since both have the meteor Z plot point. I think a redesigned bellflower is in the files too, and the plant heroes as t4s. I have no idea what it would do without just copying gardendless. Im trying to think of it getting more powerful when chilled zombies are near, maybe creating a snowstorm. Maybe it harnesses power from chilled/frozen zombies and plants, creating snowstorms that get more intense the closer the nearest chilled zombie is. Think about it like the void spell from clash royale, which can hit everything in a wide area, but has less damage if its hitting more things. Likewise, snowdrop would create a weak but large snowstorm when the closest chilled zombie is far, but the closer it gets the more concentrated the snow is, eventually chilling by itself with the snowstorm. Higher forms would be able to target further zombies while still retaining strength relative to the closest chilled zombie. Im not sure how versatile this mechanic is, maybe this is just its own tier 2 and thats it, and some other t1 snow attacker would be added instead.
Iceberg Lettuce- It feels really weak honestly, especially with how many zombies there are. I think its fine because it encourages you to merge it but I really do think that if youre bringing an entire seed slot for an "instant" use staller that costs sun it should be able to hold at least one zombie permanently if replaced. I also feel like snow pea and cold slaw are really just not very unique. At least numbing cabbage and iceweed are unique since numbing cabbage has more range and damage, while iceweed can hit more zombies at once. I suggested in another thread that cabbage evolutions make bigger cabbages instead of just throwing more, which would allow the cabbage to deal splash damage similar to melon pult, or in this case, winter melon. Going back to iceberg lettuce though, its also currently the only elemental to only be 25% (or 1/4th) a part of its families (whereas gremonade and lightning reed are 50% or 1/2 of their tier 3 elemental families) which I find strange, although I assume they wanted to make it different since dangerine inherits splash soley from gremonade's extra area and not as a base effect of any of its t1s, so using winter greens instead of blockwood as the pure fusion for the cold t3 family just makes every elemental t3 do splash damage. Going back to the plant itself though it would be cool if it could freeze water like the ice monkey in btd6. I know this is like the 4th amphibious plant i'd be suggesting at this point but- cmon- if youre gonna remove lily pad at least let us freeze the water 
Poison- 2 plants
Poison ivy- I honestly a second groundcover plant like spikeweed would be interesting to see. It would most likely inflict a damage over time debuff too, so it wouldn't need to be paired with a wall to be most efficient. It could make other poisonous plants like shadow shroom, and also provide us with other pvzh plants like poison oak.
Lime bomb- I really hope this thing ends up making dragon bruit. Maybe as a tier 3 between like, seed spitter, threepeater, and whatever shadow tier 1 we get if we do get one? I know they want to keep tier 3s down to consisting of 3 tier 1s at most so they can have some semblance of identity and they cant just roll a random 4 plants and make weird garbage that doesnt work, which I applaud. Maybe remove seed spitter at that point or just use it being a tier 3 as an excuse to have 3 heads without threepeater. Alongside dragon bruit I cant wait for kill lime pie, I think everyone has been waiting for it. Definite posterboy of promising design. My only issue is that as a trap plant its just so dang similar to iceberg lettuce and potato mine- its really just mimics them in its pure fusions and uh... has nothing else except dangerine so its really hard to say anything, especially when potato mine really doesnt have many evolutions to differentiate itself from the other two. I think lime bomb could also be used to make lava guava, and maybe be more similar to it by leaving an acid puddle on defeat, that way it can be more unique and appealing. I also came up with the name "Lemonition" which is kinda similar to gremonade, maybe that could be a different tier 2 for lime bomb.
Fire- 2 plants
Cinderwood- From what we know, cinderwood isnt going to focus entirely on boosting peas but moreso on its special abilities from pvz2, those being its incredible health, melee damage, and jalapeno explosion on death. While I feel like a wall with a mild melee chip damage is just a weird endurian/lychee it is interesting and unique. I just think as a wall it should at least have the creative freedom to focus on its tree traits, and not just the fire traits. Im glad its doing more than just boosting pure peas which right now is just one tier 1 and you cant even evolve it with other plants. I did make more t1 peas to make torchwood more interesting but it may not even need that. 
Hot Potato- When you level up hot potato in pvz2 it gains the ability to break more obstacle types. I think, regardless of level, it should be able to break more obstacles, notably saganaki blasts. Allowing it to "live" longer on higher hp obstacles allows it to be evolved. Giving it a proper lifespan and not making it an instant use is perfect for what pvz3e is aiming for

Melee Instas- 5 plants
Buttercup- Buttercup feels too similar to wall nut so I want to make it one time use. As compensation, it will be completely free. I know people dont like free plants, but I think the cost of a seed slot is very relevant here, especially since it will have a decently long recharge. I dont want to make kernel pult a tier 1 either because its frankly just cabbage pult but slightly different, and I have another lobber in mind and I find 3 good for now. It can evolve into plants like kernel pult, butternut squash, cob cannon, cornfetti popper, buddah boom, and more.
Squish- I really don't think squash should be a tier 1. It's always been just profoundly outstanding and I think making it a tier 2 removes the design philosophy of just increasing the area of effect for each subsequent tier which I find lame. Squish can evolve into plants like winter squash, butternut squash, smashing pumpkin, and hammer shroom.
Devour Bloom- Devour Bloom is capable of instantly defeating a limited number of zombies on one tile before disappearing. Devour bloom will evolve into chomper at tier 2 of course, alongside other plants like snap pea (which I think should be made with pea pod, if possible), olive pit, and toadstool.
Stallia- a tier 1 instant use plant that starts with a 3x3 area of effect- stallia is a more "watered down" insta, not being as strong but still having a good area of effect. I could see it evolving into shrinking violet, dazey chain, stunion, tomb tangler, and maybe vamporcini. I also want to mention shrinking violet since it was a contender earlier as a t1 but it felt awkward so I move it to Stallia's tier 2. I think keeping the 3x3 area gives stallia an identity, and shrinking violet is a purple flower just like stallia, and slows zombies down while also reducing their damage. Double stall! Shrinking violet could evolve into plants like hocus crocus, thyme warp, gold leaf, and, it could be used to create growing plants, like Strawburst, Kiwi Beast, and maybe even Ultomato. Maybe that could be a family- shrinking violet + a mixed tier 2 with seed spewer, since theyre all fruits, and theres 3 of them which is how big families like that usually are. The mixed tier 2 for kiwi beast could be called "stall nut"- I think that has a nice ring to it!
Gripevine- gripevine represents ill tempered grapes- when a zombie approaches it it will launch a piercing grape from the vine, having a total of 3 before expiring. It evolves into plants like grapeshot, sour grapes, grapes of wrath, and blastberry vine.

Now going back to some plants I want to add to previous categories ive covered- rounding out pults and all of the elementals to 3 plants a piece.

Pults- 1 new, 3 total
Blast Bush- Blast Bush is a tap to use tier 1 that launches berries at zombies. Blash Bush evolves into plants like Strawburst, Banana Launcher, Boom Balloon Flower, Missile Toe, Holly Barrier, and more. 

Electric- 1 new, 3 total
Zapricot- Zapricot targets the zombie closest to your house with a lightning strike. Evolutions include meteor flower, electric blueberry, homing thistle, laser cattail, and more

Cold- 1 new, 3 total
Pointsettia- pointsettia uses its sharp petals to attack nearby zombies. It has a heavy attack, meaning it works best when it can kill zombies in one hit, like bonk choy's uppercut. However, it also pierces and freezes, and can only hit very close zombies, so it wont be hitting zombies eating a wall nut. It will still hit the whole group afterwards, so its not uncommon to use them together either. Pointsettia can evolve into plants like holly barrier, jolly holly, and chard guard.

Poison- 1 new, 3 total
Tarlic- Tarlic is not quite your regular garlic- tarlic glues zombies mouths shut after being bitten. If nobody told zombies eating tar is bad, well, they're gonna figure it out shortly after due to the damage over time they take from this effect as well. Despite tarlic being a wall, its got as much health as your regular plants, meaning that too many zombies can take it out easily. Evolutions would likely include gumnut, olive pit, and cran jelly.

Fire- 1 new, 3 total
Burnsai- another tree, but burnsai is different. Actually, its going to directly steal all of cinderwood's current abilities, so I'll explain the new cinderwood here since burnsai is explained where I previously explained cinderwood. Now, cinderwood buffs projectiles again. I think its fine since when you get cinderwood, you already have peashooter, repeater, and gatling pea guaranteed. I guess it also buffs the other tier 1 peas too. However, evolutions will increase the types of projectiles it can boost, or what effect the boost causes. For example, the tier 3 of cinderwood will be able to boost Dangerine, despite it being a fruity mushroom. I think this is fun because it allows you to mix up your strategy mid level based on how many cinderwoods you can afford, starting with pure peas and getting your other plants in on the action later. If that isnt enough incentive to evolve them, I think maybe cinderwood could have a limit to how many peas it can light up via a fuel generation/limit system, say the tier 1 has a capacity of 5 peas lit and generates new fire every o.4 seconds. Back to burnsai- it could evolve into plants like inferno, gravitree, wasabi whip, and maybe even plantern. 

10 new tier ones for a total of 36 tier one plants so far. Did I miss any you want to see in the game?

Counting again I have 39 plants so im gonna be finishing up the roster with two more groups of 3 

Cosmic- 3 plants
Cosmic, while being an element, doesnt affect any group of zombie positively or negatively. 
Noctarine- Noctarine is going to be the base for shadow plants. I chose noctarine since it provides a temporary buff and thats how I want shadow plants to be. Noctarine will have a mediocre cooldown, meaning you have to manage getting new shadow plants and boosting them. It can be used to make nightshade (bop choy), shadow pea, moon flower, murkadamia, gloom vine, shadow threepeater, and dragon bruit (shadow threepeater + t2 seed spitter)
Cosmoss- Cosmoss will not create plants, but environments which kinda act like flower pots from pvzf. Familiar environments like coffee grounds, solar winds, and the red plant-it will be available. Gameplay wise, they will sit on tiles similar to craters from doom shroom in pvz1, but they can be planted on and boost plants of a family. In order to create tier 3 environments, you can just place the other tier 2 plant in the environment and it will be absorbed.
Starfruit- Starfruit is the identity of strange shooters, and its tier 2 gimmick is that it floats- making some existing plants like rotobaga. Im not really sure what else it could make but I think a friend that can float on water or whatever weird tiles face us would be a way to give those gimmicky gaps some growth- not just a hinderance but an opportunity.

Desert- 3 plants
Desert plants dry up the already dead denizens of the dunes, dealing reduced damage to them while reducing thier speed in a 3x3 area around themselves. 
Sand Grain- Sand grain is a defensive plant that grinds up grains, creating protective dust shields on your furthest plant (bar some, like traps) to the right. I actually decided on a tier 3 for this one called grainstorm. Evolutions would be with elemental plants that provide elemental shields that can apply freeze, poison, or whatever status effect you want to biters.
Tumbleweed- a wiry warrior with a wallop, tumbleweed will roll down lanes just like the old days, but this time with a proximity detection. Tumbleweed will create plants like bowling bulb (with pea pod), cran jelly, and even the new cactalog!
Hokey Pokey- we were all disappointed with the glow down cattail got in pvz2- outside of china it didnt even show up! While homing thistle is just as beloved, I hope Hokey Pokey will be just as welcome to the roster in pvz3. Outside of making homing thistle, it can create plants like MayBee, Galacta Cactus, Heath Seeker, and other familiar faces. Hokey Pokey itself acts like homing thistle, just with a range limit. Higher tiers have higher range, allowing the lower tiers to stay relevant dps wise while the higher tiers serve a purpose once you get planting in the back lines.

And thats it!

If you have any questions for how to make a plant- feel free to ask and ill make a formula for it. I cant remember everything off the top of my head right now but just about every world plant from pvz1 and 2 should fit in somewhere. 

For fun, im gonna finish this off with the method to create every plant from pvz 1 and 2's adventure, as well as some more, using these 45 tier ones! 

Peashooter- tier 1
Sunflower- tier 1
Cherry bomb- lime bomb + hot potato
Wallnut- tier 1
Potato mine- tier 1
Snow pea- peashooter + iceberg lettuce
Repeater- peashooter + peashooter
Chomper- devour bloom + devour bloom (actually want to mention devour bloom will be renamed to snap trap, and create plants like snapdragon)
Puff shroom- tier 1
Sun shroom- puff shroom + sunflower (I dont like how sun shroom currently outclasses sunflower in an absurd amount of ways any time its viable, which is exactly always and only in the sewer. Especially since sun shroom doesnt compromise your offense by having merges that dont produce sun and just do damage, its just sunflower but for sewer. Making it a tier 2 also lets it retain its growth gimmick, and serves as a tutorial to tier 1 puff shroom by showing that puff shroom evolutions can be powerful, but they dont gain new gimmicks and lock you out of more powerful tier 3s)
Fume shroom- Puff shroom + spikeweed (I feel like fume shroom is close enough to chainsaw grass right now to justify this, and both spikeweed and fume shroom countered screendoors in pvz1. I dont know if this conflicts with quiller queen, as for the acid shrooms I would just adjust them to be t2 puff and a mixed lime bomb evolution to make those more consistent with the cold leaves)
Grave buster- tier 1 (Grave buster serves as another anti grave option other than potato mine, as well as the vine base. As well, grid items will be divided into hard and soft grid items, with hot potato excelling against soft grid items like cheese and octopi)
Hypno shroom- puff shroom + solar sage's tier 1 (still dont know what im gonna call the tier 1 for this. Frankly it could just be sage sage from pvzh, I know that has a sun related ability so that works for me)
Scaredy shroom- peashooter + puff shroom (honestly I was trying to figure out how to work the hiding gimmick into it but then I realized I would need an ENTIRE tier 1 that just hides and thats too much work for one plant (two if you count cactus but I have a plan for it anyways)
Ice Shroom- iceberg lettuce + boom shroom (maybe winter greens + boom shroom's tier 2)
Doom Shroom- tier 3 boom shroom (maybe tier 2 could be called loom shroom? like looming doom or something? It would make sense since explosive plants no longer activate instantly, it would loom in the distance waiting for a zombie to approach)
Lily pad- the first plant im gonna take out entirely. I know they said they wanted to add it, I just dont see it being different enough to tangle kelp, especially since they removed tangle kelp's stun. They also want amphibious plants to be amphibious, and i just dont see lily pad working on land. The only thing I can think of is making it a tier 2, who instantly uses its pvz2 plant food when merged and creates more lily pads.
Squash- Squish tier 2. Wanna mention winter squash here since I had a lot of fun concepting it a while ago but I never posted it here- its ability would chill zombies that survive, but also fully freeze already chilled zombies. Im not sure if it would be a tier 2 or 3, probably tier 3 to get that 3x3 area from winter greens, and it frankly might be too good at tier 2. It also has the same identity crisis nippy cabbage has where its just an icy bonk choy despite being a sidegrade and not an upgrade, so making it a squash upgrade makes the most sense. Besides- winter greens + squash sounds a lot more accurate than iceberg lettuce and squish. Anyways-
Threepeater- tier 1. I think the only way threepeater can be more than just three peas in a trenchcoat is to be its own thing. Likewise, its gonna be efficient- 225 sun, but only the middle head can see. In a game where every plant can just be stacked up to 4 of itself, threepeater is gonna have a lot of competition from every single attacker, and especially with how tiers scale stats right now it really needs to be cheap or its just three tier 1 peashooters, when you could be 3/4ths of the way to a tier 3 instead. I guess it would be a tier 2, but theres a lot of plants like dragon bruit that I dont think work at all unless threepeater is a tier 1.
Tangle kelp- tier 1
Jalapeno- Hot potato + tumbleweed. In pvz1, cremator damage ignored armor, and while thats basically never relevant because basically every armored zombie is one shot by anything that does cremator damage regardless, I think hot potato specializing in soft damage could retain that gimmick, sorta like what spikeweed has right now.
Spikeweed- speak of the devil- tier 1. Also want to mention that spikeweed feels kinda weird right now, so its getting some more damage in the form of secondary damage, specifically after it gets merged. Secondary damage affects armor, and the primary damage remains on the tile the spikeweed is on (for groundcovers). This should help its gimmick stay relevant without making the plant utterly useless the minute you have anything that already chews through the armor before the zombie dies, which youre gonna have to for non horde zombies anyways. The formula I worked out for this was (1.5x spikeweed purity + 0.5x tier), so for example, spikeweed would be 0.5 + 1.5, 2x, pine needler would have 0.75 + 1, 1.75x the base armor piercing damage as secondary damage. Endurian would be 0.375 + 1.5, 1.875x. Hopefully that isnt too confusing and the values can be adjusted but hopefully spikeweed purity is still valued while tiering up still feels like a reward.
Torchwood- tier 2 cinderwood. Again- burnsai is replacing the current (speculated) cinderwood, and while that can boost peas like the original torchwood, as a tier 2 torchwood can light up tier 2 projectiles, like popping corn kernels, grilling melons, and setting some spore aflame. It can also deal damage to zombies floating above it.
Tall nut- tier 2 wall nut. 
Sea shroom- tier 1. Im pretty sure this guy can be used out of water in pvz2, and if he keeps his splash damage he could serve as a unique plant due to its significantly slower recharge rate. I was planning on making it just an amphibious form of puff shroom that had different merges because that would just be a neat niche for an amphibious plant, but that meant puff shroom would be able to make two heroes as nightcap uses tier 3 puff shoom, and citron uses tier 3 sea shroom, although again heroes arent in the game and neither are most of these plants. If I did it my way though, id have to separate these plants, which im fine with anyways
Plantern- another plant im gonna avoid for now- fog worked in pvz1 because it was a lot more relaxed and it added to the atmosphere. Its kinda something that only really works the first time. I know theres some stealth zombies coming up, so maybe this could be a cowbell evolution- theyre kinda the same shape and plantern would be good for revealing stealth zombies. I think it does that already in pvz2c. In that case it would probably be cowbell and e.m.peach, its fitting as an electric plant and the recharge gimmick would be a nice way for it to not just fully consistently remove an entire mechanic from the game. I feel like right now too much of the game focuses on negating gimmicks instead of playing with them, forcing you to use a specific plant to just remove the uniqueness of threats. Having plantern need to recharge allows it to do what it needs to and allows you to use multiple at once.
Cactus- Scaredy shroom + hokey pokey tier 2. I know hokey pokey has homing akin to homing thistle but I think that could be the "downside" or the "watering down" provided by puff shroom- losing that. I know theres also the whole mushroom thing and day time, I think that could be absent on plants that are only 25% mushroom. 50% and above though would be fair game for whatever they want to do. Honestly just making them slowly fall asleep over time instead of just always being asleep or straight up just dying is a good compromise, and maybe they would wake up if something happened nearby, like something getting crushed by a bowling ball. It also gives scaredy shroom's hiding ability some relevance to mushrooms and this new danger proximity gimmick. 
Blover- tier 1. Again as instants are no longer actually instant, blover constantly blows back zombies a little bit- kinda like the first comic where they blew for an extended amount of time without disappearing.
Split pea- bop choy + peashooter. Im fine with it being this weird middle ground option for when you dont know what to put down in the middle of your defense, and as a tier 2 its still gonna have better stats. Actually, I had the idea that it could turn around when zombies are close by and theres nothing behind it, it was a buff for pvz2 split pea I was discussing with someone making a mod.
Starfruit- tier 1. Like threepeater I dont see this doing anything if its not a tier 1. As a cosmic element, I think it could float, which makes sense considering we already have plants like rotobaga. 
Pumpkin- grave buster +  squish. Both squish and pumpkin are gourds, and I think it would be interesting if squish had more health than other instas, serving as mini-walls against projectiles and ranged threats before they go off squashing. Wall nut was the other contender but that just felt boring.
Magnet Shroom- Puff Shroom + E.M.Peach. I actually was struggling with this one and I was fine with omitting it because it frankly only worked in the first game since it was a lot more lax and wasnt as big, and as a mushroom didnt just immediately invalidate anything with metal as long as it wasnt night. However I feel like this combo just works really well- I didnt plan this out, but magnet shroom is electrical, and has to recharge after taking metal. It just feels too good to pass up, even if im not really a fan of magnet shroom. Maybe it can have tier 3s that make it more than just ripping the majority of health and offensive pressure from nearly everything actually threatening.
Cabbage pult- tier 1
Flower pot- Another plant I don't think needs to be in the game. I like the idea of flower pot- it adds a baseline cooldown to expanding your setup and an extra cost to instants that might make you sacrifice a pot or have it in an awkward spot. However in pvz3 theres just about nothing for it to do. Actually, it could be useful against esgargot's slime. I just cant think of any way to make it- maybe grave buster (in vine form, of course), and spikeweed?
Kernel Pult- cabbage pult + buttercup- I think this needs to be a tier 2 for the same reason threepeater needs to be a tier 1- unlike threepeater, it doesnt do more. It actually does less- and disregarding the butter I feel making it a tier 1 just means you have two families of pretty basic lobbers, but one has butter and the other doesnt. That just doesnt sound fair to me. It also sets up cob cannon to be a tier 3 just right, akin to gatling pea.
Garlic- This is the one plant I would never add to pvz3e. It barely exists in pvz1, doesnt work at all in pvz2, and in pvz3 youd have to make multiple plants who's entire purpose is putting zombies in other lanes. It just doesnt feel right. If you really want it, it could be tarlic and blover. Frankly I made tarlic SPECIFICALLY to remove garlic from the game (well, my version of the game, at least)
Coffee Bean- Sun bean + stallia. Coffee bean's role has been changed to a support, giving zombies an immediate caffine crash upon consumption. Honestly I dont know what this would do. Maybe it would make them eat faster but do less damage, benefitting plants like endurian? Maybe it could satiate some zombies, like newspaper zombie. 
Umbrella leaf- tier 1.
Marigold- stallia + potato mine. Marigold now releases a golden nova that gilds weak zombies, sorta similar to ice bloom in pvz2. Potato mine is one of the few plants that distinctly displays metal in it, and I think that could be a core part of it's identity. Frankly I wanted to ditch marigold, but theres a few plants that would really appreciate it existing. If that ability doesn't do well, maybe it could gild obstacles, or even hard armor, softening them. If you want to use hot potato in a level with hard obstacles, now you can! 
Melon pult- Seed spitter + cabbage pult. Seed spitter brings aoe, and cabbage brings heavy single target damage. The perfect combination to make the livid lobber we all love. Making it a tier 2 also puts winter melon easily at tier 3, like gatling pea and cob cannon before it.

Those are all the adventure plants, but I wanna do a lightning round for the extras, so im not gonna put any that are already in the game
Twin sunflower- going back on that immediately but I do want to mention that despite it being an upgrade plant, Im not going to change its recipe into a tier 3 like the other upgrade plants.
Fume shroom- tier 2 starfruit + fume shroom - this octo-ordinate oval deserves a spot at the top, and it clearly shows us why in pvz1. Hopefully it might be more balanced as a tier 3, especially one that gets watered down a bit by puff shroom. Im also going to be changing phat beats just a tiny bit to make these two more unique- so watch for that in my pvz2 plants post after this one.
Cattail- I think theres already a plan for this to be a pure tier 3. I dont have whatever cat plant the tier 1 is but to be fair I wanted 50 tier 1s, so adding the new stuff thats been revealed since I started this project, like cowbell and the tier 1 cat is pretty likely to end up in this roster once those come out.
Spikerock- marigold + sawgrass. Another metal plant, at least its always looked partially metal to me. I know he has a rock band as of pvz2. I actually just looked it up- its a metal band, as he is "the most metal plant". Spikerock could take after its pvz2 plant food effect, serving up spikes to zombies through the lane akin to sawgrass. If we go off of marigold's ability that afflicts weak zombies, this plant could serve as a decent counter to disco zombies, which should totally be a rivalry! Im surprised they arent rivals, since spikerock easily deals with the swarmy spawns, but disco can spawn them past spikerock once it approaches. 
Gold Magnet- I know tier 3s only consist of 3 tier 1s. In that vane, theres no way to make this work. The only change I can think of is changing magnet shroom to potato mine instead of empeach, which I guess works since potato mine does extra damage to hard objects like armor (particularly esgargot's but I think it still makes enough sense- I mean in pvz2 the dark dragon was weak to magnet shroom), and its metal. I prefer the E.M.Peach recipe, but if we double up on the potato mines that gives us 2 in the gold magnet recipe and doesnt mess with spikerock, since sawgrass is the pure t2 there. I dont think we have any tier 3s where two impure tier 2s each share a tier 1, but I dont think that bends the rules too much and ive been wanting to see it. Personally, snow sling pea and electric bamboom are ones i'd enjoy a lot!
Winter melon- Winter greens + melon pult. Just like winter squash, it just works. The names, the abilities, its perfect. 
Cob cannon- Kernel pult + kernel pult. As the only upgrade plant to require two consecutive plants, both being a plant that I have as a tier 2 here, it just works out wonderfully to have it be a double up of kernel pults. This might leave cornfetti popper with some trouble getting into the game, but I can probably figure something out. 
Imitater- honestly I wouldnt mind imitater as a power up. As for how it works, it just becomes the last plant you've planted. I could also see it being a "tool" plant, in that case, lily pad could return as one, though I dont have many others in mind.

For my (maybe) final post here im gonna go through pvz2's adventure and maybe do some seediums and other plants. Im gonna be using an image from Vander Graaf that has 2's adventure plants without any of pvz1's plants, so if I go a bit out of order thats why

Starting off... phat beet is being replaced with cowbell. Ill probably add the other plants that are coming with the new update to the roster, I did want a clean 50 but I couldnt come up with another category. Also, devour bloom is being renamed to snap trap. I just like it more and I want to make snapdragon with that. Finally- all the primal plants will be excluded. Primal sunflower just doesnt really need to exist, primal wall nut's whole gimmick (well I guess surviving crush attacks, but I mean the higher cost with lower cooldown) doesnt work if it just is a wall nut evolution, and primal potato mine is basically just devastater- and at that point including primal peashooter feels unfair.

Bloomerang- Jumbrella leaf + pine needer. Realistically this would be like, an actual tree, but I guess thats what snow conifer already is. Im pretty sure theres some pvz2 mod that gives bloomerang some umbrella leaf abilities so this would be a neat nod to that.
Iceberg Lettuce- tier 1
Bonk Choy- tier 2 bop choy
Snap Dragon- Snap trap + burnsai
Spring Bean- blover + sun bean
Coconut Cannon- Ca-boom + blast bush + wall nut. Ca-boom is my version of slaw slinger, who has splash damage instead of faster firing.
Chili Bean- tumbleweed + sun bean. Other than the desert element, I feel like it would be fun to give it a tier 3 with jalapeno added, which means they need to share something. Maybe the gas cloud would be changed to a rolling gas cloud, and tumbleweed can stun zombies so I think this works out well enough. Then again, being a sun bean evolution it could be more creative, maybe the zombie who eats it doesnt die instantly, but farts when hit? I guess the original function could be returned with the aforementioned tier 3.
Lightning reed- tier 2 zaptail
Pea pod- tier 1. Especially in a game with evolutions, this cannot exist outside of being a tier 1, and I have some fun evolutions for it. Also quick reminder (actually I dont think I decided this at the time yet) that pea pod itself will only have 1 head max, while tier 2s have up to 3 heads (think dazey chain, bowling bulb), and tier 3s can have up to 5 heads. Heads will be gained by adding the other tier 1(s) to the plant, for example, dazey chain gains a new head each time you plant a stalia on it, up to 3 of course.
Hot potato- tier 1. 
Pepper pult- cabbage pult + hot potato. I want to use hot potato here since thats what I used for jalapeno. Actually, I wanted to replace burnsai with a new pun I came up with- haburnero, but habanero peppers are actually spicier than jalapenos so I guess that works as a tier 3. I guess a tier 1 with a pure merge into jalapeno would work better for chili bean, but nothing's clicking with names yet.
Chard Guard- Tall nut + spring bean. I just think it would be interesting for chard guard to be a tall plant, especially thats not just tall nut's gimmick anymore. It also kinda gives spring bean that sequential 1 > 3 > 5 thing that the tiers do, although delayed a tier. Making it naturally regrow leaves should make it feel unique compared to other knockback plants and tall walls.
Stunion- stallia + puff shroom. Bigger stun, but you lose some area. Perfect for a puff shroom evolution. 
Rotobaga- starfruit + peashooter. As a tier 2, I think going from 5 to 8 projectiles is sequential enough. It also floats naturally, which is what im looking for with starfruit's evolutions
Red stinger- this entire plant's gimmick is just being a simpler version of this game's whole premise. While Im not against adding it, I dont have any recipe for it in mind, which I think is a fair excuse to just axe it. Wish that wasnt the case since its pretty popular, though.
AKEE- Either the pure tier 2 for seed spitter, or seed spitter + threepeater. I think a familiar face would help seed spitter gain popularity, but regardless it keeps that, and its probably better to give brand new tier 1s brand new pure evolutions
Endurian- lychee (wall nu + spikeweed) + tall nut. I know this one's already in pvz3e, just wanna cover everything since I usually have something to say. I think endurian is perfectly fine right now.
Stallia- tier 1.
Gold leaf- Cosmoss + Sunflower. I know I said the pvzh environments would be represented- solar winds will be a tier 3, created by planting a twin sunflower onto a tile with the gold sun tile.
Laser Bean- 
Citron- to avoid confusion, Citron (pvz2) will have a new name. I personally enjoy Cytrus. Anyways, it would be made with electric peashooter + the tier 2 pure EMPeach. Its also gonna have a small electrical aura that can fry up weaker zombies, to make it able to hold its weight as a tier 3 in a game with pigeons and chickens.
EMPeach- Yes I know it has periods im just too lazy to put them. Tier 1. Instead of being an instant use plant, it unleashes an electrical nova when zombies are near. EMPeaches can only evolve while at full charge, and begin at full charge when planted, hopefully upholding its original function of stunning mechs (per my elemental rework) while being a bit more versatile.
Infinut- EMPeach + Wall nut. I hope as a tier 2 it can actually have enough health to do something meaningful, instead of just kinda being worse than wall nut since a regrowing wall nut aint that great if everything behind it gets eaten. Maybe it unleashes an electric nova when "eaten" as a last resort.
Magnifying Grass- Sun bean + tumbleweed. Since sun bean is a direct parody of sun beam, I think its the best sun producer to represent a prism plant. As a glass plant, I think that it should be made with a desert/sand plant, and I think tumbleweed fits the role of single use investments perfectly in that role.
Tile Turnip- No plant food, no tile turnip. Its sad, but simple, and I really have 0 idea what it could actually do, and  just like red stinger, I conveniently just dont have any clue how it would be made either. I guess cosmoss would be a good start.
Sun Bean- tier 1. 
Phat Beet- Cowbell +  Squish. He sorta slams himself when he attacks so I think squish works. As for the cowbell integration, he can hit invisible zombies with his sound attacks, and specializes against them by critting nearby zombies, so he should excel at taking out squishy melee units that rely on a gimmick he ignores. When I made fume shroom, I said I'd make phat beet special. What I like to suggest for people making pvz2 mods is to make him shoot a sound wave, which crits if it only travels 1 tile or less and does aoe damage. I think he could do that here too, but im not sure how the recipe would integrate a projectile. I'd make it a tier 3 at that point, but I want kiwi beast to be a tier 3. Just some extra food for though. 
Intensive Carrot- another plant that doesnt work in 3e- you'd have to put something on the defeated plant's tile to make intensive carrot, or it would be a tier 1 which would absolutely not work, especially pure fusions. I could see it being like banana launcher, where you can pick a plant to revive every 40 or so seconds. In that case, it would probably be related to aloe and blast bush
Spore shroom- I just personally dont like spore shroom. It alone as a concept just disrupts the fundamental balance of the game and its nearly impossible to give it an actual role without it being overpowered or completely useless. Its not just that its a snowball but it just gets so many opportunities to where it either just takes over the entire lane or is completely negligible. Maybe if it made a different mushroom, like boom shroom or puff shroom, similar to witch hazel. At that rate, it would probably be an upgrade to pult shroom. 
Celery Stalker- Bop choy + Wall nut. I think any classic incorporation of just bop choy and wall nut straight up wouldnt work. Celery stalker acts as a way to block off further zombies from advancing while dealing excellent damage to the target that has walked past it. Maybe to play a bit more into their cautious nature, they wont appear while they are being stepped on. Seeing the price hike from 50 to 150, it makes sense to try to remove this issue from it, and it also makes the plant more unique in my opinion.
Thyme Warp- Gonna axe this one too, sadly. I mean it could be the tier 3 stallia and be limited to the 3x3 area, but this is a plant that only works in NMT. They could remove that, but I feel like its kinda really strong and not that enjoyable, and it also feels weird since its an instant use plant. Then again, at the highest tier, tier 3 true instas could work, compared to "temporary" plants/trap plants
quick reminder that im not doing the primal plants. too redundant for the most part. however jurassic marsh has one more plant-
Perfume Shroom- Solar Sage + Boom Shroom. Now it enchants friendly zombies (ie hypnotized zombies, zomboids) and makes them take reduced damage.
Guacodile- Tumbleweed + peashooter. I think crocodiles are in Florida. Maybe this could be peashooter + tangle kelp, to make it distinct from tangle pult. 
Bowling bulb- Tumbleweed + pea pod. 
Banana Launcher- blast bush tier 2, maybe 3
Moonflower- sunflower + noctarine. I think it would be nice for shadow plants to not rely on a specific producer, and noctarine being the tier 1 allows that to work.
Nightshade- bop choy + noctarine. Noctarine will realistically be free with a high cooldown, so the temporary nightshade should be able to hold its own with its temporary high strength leaves before being powered up with a moonflower, or just during some downtime where it can regrow its leaves back without throwing them
Dusk Lobber- Seed spitter + noctarine. This could frankly be a tier 3 with how strong it is, and it probably wants to have SOMETHING to do with cactus/hokey pokey since it IS a cactus. Maybe this recipe, then add double hokey pokey. 
Shadow shroom- boom shroom + noctarine. Shadow shroom has always been a mediocre chili bean unless you run some really weird strategy with like, garlic and chard guard. I actually did it once it was kinda fun but it got overran by any density or threat and basically every world without either had a way to counter that or was just already too easy to consider proper strategizing. This version would explode into a poisonous spore cloud that poisons zombies. When powered, these spores grow on zombies which can be passed by contact.
Grimrose- snap trap + noctarine. Its that whole 1 > 3 > 5 succession thing I talked about earlier, but of course, with the shadow element incorporated. Maybe to make it a bit more interesting when unpowered, it would target the highest health zombie in the lane, or maybe most dangerous like dartichoke, and deal damage to zombies in between with its little shadow path it casts.

And thats it! Later I'll do premiums and seediums, so if you want to see any feel free to comment! Again, just doing this for fun, and i'd love to hear what the community thinks about this roster, and any other tier 1s I could add. Im still looking for 5 more tier 1s, and while some are already projected I think I still have some slots left. Maybe some vampire plant for the likes of vampweed and vamporcini? I could do another plant of each element (except cosmic) for 4 choices per element. Definitely gonna do at least one more amphibious plant. Comment your favorites!
Edit: forgot intensive carrot. oops!

Gonna wrap this up with some premium plants. After seeing the new baneberry I just had to come and add it to pvz3, since my pea pod is tier 1 its perfect!

Snap pea- pea pod + snap trap- I think the issue with snap pea is that it often shoots a head at a zombie just to eat it anyways, making it a chomper (or toadstool) thats just weaker because it has more mechanics that just dont do anything.
Shadow peashooter- another classic, THE classic! From what I recall this was the first seedium added to the game. Made with noctarine and peashooter.
Shadow threepeater- not a seedium but I just want to add it here because it stems directly from one- this would be made with threepeater + noctarine. I think its fair enough, since threepeater is a lower cooldown plants, so you can either put multiple shadow peas to stack damage in a lane, or go for the efficient coverage of shadow threepeater. It also makes our next plant-
Dragon Bruit- This would be created with shadow threepeater as well as the tier 2 for seed spitter. Whatever fruit flinger falls from the tree is bound to lob just like the lemon before it, so it would fit perfectly making dragon bruit. Another idea I had was to make the pure tier 2 the pure tier 2 for noctarine. In this case, on defeat, instead of baby dragon bruits it will drop noctarines, which will temporarily boost parts of your lawn. 
Baneberry- pea pod tier 2 + pointsettia tier 2. Poinsettias have berries and both baneberry and pointsettia slow zombies. I was going to use tier 2 stallia, but that makes less sense than a plant with berries, and I want stallia's tier 2 to be shrinking violet which just makes no sense!
Ultomato- pea pod + e.m.peach. It has the straight shooting abilities of pea pod as well as the stacking ability, and a long cooldown between attacks like empeach. Its even the same filamint family!
Zoybean Pod- pea pod + 
Solar tomato- solar sage + stallia. Stallia gives it that 3x3 area and stalling capabilities while solar sage is a temporary sun producer. 
Electricitea- lightning reed + chili bean. Both electricitea and chili bean kill the zombie that eats it, and electricitea can hit other lanes while chili bean only hits its own. In Pvzh, lightning reed is classified as leafy, so the genetics make sense too
thats all ive got for now but if you have any suggestions id love to do em!