WARNING- I think some of the content discussed here is leaked but honestly I forget

I think the tier 4s should be the heroes from plants vs zombies heroes. Also, I think making them combinations of pure tier 3s would be good for a couple reasons. For one thing, I want each plant (at least, as its own tier 1, 2, or 3) to be something that plant hero can use in plants vs zombies heroes, one from each of its classes. It also makes it a lot easier to only have each tier 1 capable of making one hero, so that no tier 1 is better strictly than another because it makes the most tier 4s. Finally, it creates a pattern that prevents tier 5s from existing while still making sense, since tier 1s can have a max of one tier 1, tier 2s can only have a max of two tier 1s, and so far (and from what I've heard this is intentional) each tier 3 can only consist of 3 unique tier 1s. Bringing it back down to two creates a pattern, and since following that means tier 5s would consist of 1 plant each, they arent possible to make due to tier 4s always having at least two tier 1s. I find this fitting as heroes should really be the highest tier and prevents balancing issues with allowing players to just get higher and higher and higher tiers that have to be unique and strong and would end up just trivializing the game, and preventing players from spending excessive resources in unviable ways that would cause them to get stuck.

As for the heroes themselves:
Green Shadow - Gatling pea is obvious, and I want to give her winter greens to reference her Big Chill power.
Solar Flare- I have to go with sun tower for solar, but for kabloom im not sure. I did come up with a kabloom plant a while back in the r/pvzh discord called Burnsai- another flaming tree plant, but this time being a bonsai redwood. I know this is what cinderwood is speculated to do instead of boosting peas like torchwood always has, but I think burnsai could be a tank that burns up overtime before exploding in a fiery sacrifice- Banzai, as they say in the movies! As for cinderwood, I think it increasing the projectile types it can boost each tier would be fun- when you only have tier 1 cinderwood you will have every plant it can boost- peashooter, repeater, and gatling pea- from the tutorial, although if im making new plants I also have tier 1 pea pod and threepeater as peas. As you get plants like torchwood and the tier 3 however, you could see it boosting plants like Dangerine. This would mean theres 3 fire plants- but I dont mind- I think just two isnt going to be enough for each element if I keep making more plants in What I would do in terms of the roster | EA Forums - 13556213. 
Chompzilla- While chomper isnt in the game yet, im picking it as the solar representation. For mega-grow I can see pea pod being a choice since its notorious for growing large like chompzilla. I really have no other ideas outside of pea pod though. However, I do like it since so far I think a lot of these heroes are like super versions of tier 2s that wont really get tier 3s- in this case snap pea. I think snap pea being made from chomper and pea pod would be really cool, since it would be able to eat enough zombies to actually kill something with the spit heads after gaining enough of its own, and not just eat a zombie it weakened and failed to kill.
Grass Knuckles- probably the easiest one- beat choy and chainsaw grass.
Captain Combustible- Torchwood's tier 3 is the obvious pick here, but for kabloom im not sure. I honestly think banana launcher is the most likely. Banana launcher would probably be the tier 2 for blast bush (like I said before, I dont mind as long as the pvzh card is in the pure line of the tier 3 at any point). I think being able to rain down meteors is really fitting for captain combustible since he literally has a meteor power! Maybe the meteor could act as a super torchwood, allowing you to boost your field based on where you need it the most!
Rose- This one is tough- I want to say solar sage for solar but I know we're getting bellflower for sure, or at least its been leaked I think? As for smarty im gonna go with Stallia, since rose is known for debuffing zombies and well, stalling. Stallia also evolves into shrinking violet which is straight up magic, so the tier 3 is probably gonna involve magic too, I just havent come up with it yet.
Citron- If we ignore the BFN design I think punk shocker is perfect with all citron's tech and lasers and stuff. Its tough to choose what to use for guardian, but I want it to be amphibious, since citron has both of the amphibious classes, and oranges/fruits are high in water content. I think sea shroom could work, since thats an amphibious guardian plant I plan to add to pvz3e. Speaking of citron, I want to rename the pvz2 version to "Cytrus"- a mix of cyber and citrus, to differentiate it from the hero Citron.
Nightcap- I cant decide between puff shroom or boom shroom- boom shroom works better imo because nightcap's signature power is literally called "mush-boom". For smarty, I want to use blover, another card I came up with in the r/pvzh discord, which is a 2 cost leafy trick that bounces damaged zombies. While its a "really conditional but really cheap" card which are usually frustrating, this usually requires you to lose plants without defeating zombies, gives them the zombies back to replay, and is really useless if it costs so much you cant even use the turn- so I think if a set 5 comes around we would totally see blover as a smarty card, which justifies it being used to make nightcap. The reason I picked blover is because of his whirlwind superpower.
Spudow- Totally a combo of mashed destruction and hot potato's tier 3. Since hot potato isnt a pvzh card yet, ill explain my idea for it here (stats approximate, of course): Hot Potato would be a 1 cost environment that deals 3 damage to a zombie there when destroyed. Yes, environments are destroyed and not just "covered", we can see this with mushroom grotto activating punish-shroom. It could even be four damage but im not sure how I feel about it doing that much, could be fine though considering it has to be played on the ground, isnt immediate, etc etc. The hope with this environment is to punish the meta environment area 22, as well as provide another cheap environment for plants. In kabloom, you also have hot lava itself alongside fireweed to easily activate it yourself!
Wall Knight- Thinking about this made me realize that there is a Juggernut in pvzh, which is different from the juggernut in pvz3e. However, the juggernut is just a wall nut in a suit of armor, which comes from a wall nut's plant food effect in pvz2! Garden Warfare even gives us a good name for this- Iron Maiden, so maybe pvzh's juggernut could get a name change. Besides that, in pvz3e, it would be made from Juggernut (wall nut's tier 3), and Astro Vera. I know Astro Vera isn't currently in pvz3e but I feel like aloe fits as a tier 1 plant, Wall Knight has the ability to heal his plants, and Astro Vera has a lot of cool tech, just like Wall Knight's armor.

Thats all of them. Some include plants that either arent in pvz3e or arent in heroes, but ive suggested ideas for them somewhere or another. Also, I dont care about beta carrotina because I really cant think of a SINGLE plant for her and if I dont have to bother then thats just good news for me. I would really love to concept her if I could but I just cant think of ANYTHING, so im going to exclude her, at least for now.