Based partly on this prompt by ericsart40, I went for something a bit more monstrous as a sort of foil to delicate/royal Prinpea. Originally a frightened little rodent-like bulb that burrows and emits a noxious odour to ward away predators. it becomes increasingly bloated in its second form, before beginning to actually use its foul breath and size to bully other Pokemon out of its way. Though it never grows very large, this Grass/Normal Pokemon eventually becomes a quite potent Grass/Poison which can even scare off some of the largest Pokemon around when they smell it coming.

Oddly, their greatest threat is humanity, who often find their root-like tails (and especially nutrient-rich tail bulbs, on the last form) delicious in meals.