That's a matter of opinion, but I think the worst Grass Pokemon is Paras, compared to all the other grass Pokemon I know of it is the worst.
definitely lillipup
entie is awesome! i think the worst is... (drum-roll) WORST IS CELEBI!!!
I think blue or red or yellow is the worst
Totodile
only the worst Pokemon AKA magikarp
Pokemon Dark Cry version.
It depends on what type you like. I'd say the worst pokemon at the beginning is turtwig but he is pretty good when he evolves into torterra. Chimchar is good and when he evolves into infernape he is a beast. So personally the worst starter pokemon is piplup.
In my opinion, it is Splash.
memento
Mewtwo.
It is mostly opinion, but the majority of fans find Magikarp the worst, as it is weak and has low abilities. You can find him when you go fishing.