Metapod

Like the real deal, Caterpie evolves first into a pupal stage, Metapod, and back when these games were new I thought it was ingeniously clever that there were "pupa" pokemon theoretically incapable of fighting, but able to keep boosting their defenses as they endured damage and gained experience points. It didn't really work that way in-game if you evolved Metapod straight from Caterpie, since it would retain Caterpie's meager attacks, but it was still a cool concept.

This is another one that just looks exactly like the real thing, except of course for the eyes, which look either sad or grumpy depending on which side of the Metapod you're looking at.