Some ideas to add...
The newspaper-zombie has at the moment a bonus of 4 ATK when hit, but i think he should do following:
In the battle-Phase, he's the first to attack
In the orignial PvZ Game he gets faster, when he'*, so thats my idea.
The old piano should actually destroy in a random row everything, because thats what it does in PvZ.
The Gargantua-Zombie should place, after loosing some health, a gnome right before him. The gnome has the team-ability. So he also acts like in PvZ.
Add the ice-shroom into the game. He freezes every zombie on the battlefield.
Add the ladder zombie, which has the team-ability and allows all zombies in his row to attack behind wall-nuts.
Add the Sun-Priest Zombie from PvZ 2 (old egypt) He steals suns from sunflowers and turns them into brains.
Add a shovel (Plants). Acts like in normal PvZ. Get you plant back and get your suns back, thats it !
Add a mage-zombie, which creates a grave, which creates a random grave-zombie.