The bosses in PvZ2 feel the same, except the Zomboss Dark Dragon, so I made some.
Baron von Bats
I feel like this would be a very good boss, or they could have him as a special boss. he would spawn zombies and teleport to move. He can also release bats like Zombie Chickens, but they don't target the lawnmowers/house, they fly in a row three times, then attacks plants if not defeated. He can make a whole row of plants disappear with his rainbow laser. he would have the same health as the Dark Dragon.
This one would be interesting, and probably unlikely, but he uses his rocket jump to move around, and use his gun to attack plants. His Zombie Stink Cloud will make him unable to be seen. His ZPG can target a plant and do a Cherry Bomb's damage, no plant can survive this, even plant fooded defensive plants. He would have 500 health.
Mutated Zombie Chicken
Way not likely, but a giant Zombie Chicken that releases lots of Zombie Chickens to the lawn. He also moves very quickly across the lawn. Also, he can fly and crash land on your plants. he would have around 750 health, only plant you get is Lightning Reed, so the chicken gets electecuted.
This fellow would make food and throw it at you, he can spawn special basic zombies and its variants with fish that they attack the plants with. He rides a Chef Gargantuar Robot and can shoot sauce that can make a row of plants sticky and can't function. Also, he will pull all plants on screen to him, if any is near him, they will be burnt in his oven body. And for a joke, he can crush plants with his butt, that are burger buns.
Plants vs. Plants
This would be unique, as you select a sun producing plant, an attacking plant, and a defensive plant, and yes, Pea-nut can be both the attacker and defensive. Then, you have to do a boss with those plants. If they do low damage, their Plant Food attack will do heavy damage, like a Peashooter, but heavy hitters will have their Plant Food attack less damaging, like Winter Melon. Other attacks would be their primary wepon and jumping on to your plants in a 3x3 area. Sun producing plants heal, and devensive plants defend, so you want those first. Some will have strict plants to use, so you can't pick. Defensive Plant Food moves are the same as in game, and sun producers heal all plants (not yours) to full health, so you might want to take this out first. A list of dangerous plants to use:
Twin Sunflower (for big heals)
Tall-nut (for having a lot of health for defending)
Winter Melon/Melon-pult (for extreme damage and Plant Food hits of your plants)
Snapdragon (for hitting in multiple rows at once and Plant Food ability can instant kill any plant except Plant Fooded Wall-nut/Tall-nut and fire based plants)
Bonk Choy (for repeated punching and a devestating Plant Food move)
Pea-nut (for both being an attacking plant and defensive plant
Sun-shroom (for not being able to defeat until its final stage and its final stage can heal quite some)
Fume-shroom (for being able to hit all plants in one row and a Jalapeno like Plant Food attack)
Probably more dangerous plants, those were some. Every plant has its own amount of health.