Uhh... Was there any other real choice for Todd, when it came to trainer type? I mean sure, most Bug Catchers usually TRAIN the bug-types they catch, but that seems like semantics to me.
It was very tempting to give Todd a trifecta of frog-type pokemon. I decided specifically on Politoed for it's matching colour scheme and almost having "toad" in the name. Croagunk looks like a creeper. Like a socially awkward creeper. Which, in many cases, is how one might describe Todd.
Grimer, though, is a nod to Todd's spitting, sliming, gunking spit. That and the fact that the boy is just not clean. He doesn't bathe, and he's just kind of... gross XD Therefor we get: Grimer. The way I have drawn Grimer here makes me think of the Smooze. The Smooze terrified me as a child. o___o