Caterpie.
BTW, do you say it PEE or PI? When I first started playing the game way back when red and blue were the only version, I said PI, and so did other people I knew, but in the English dub they say PEE. I still say PI, though, because that was what I called it long before I saw the anime.
I want my old avatar back...
I wonder if anyone will bother trying to read what this says.