Crobat
it's fast and it can use confuse ray and toxic
so your confused on the first move then poisoned badly on the second, or if you switch out that poke is poisoned (and about to be confused). hahahahahahahahaz!
plus it can learn some bug moves (x-scissor) if a pesky psychic comes into play plus i teach it fly cause that's a great stall move that makes a poisoned pokemon take damage while crobat is safely in the sky.
also i would lead with my charizard because it will pwn anything regardless of type advantage, basically i release charizard and the other trainer backs down, it's just how it works.
i used to lead with snorlax or scizor and give them a quick claw so they might get the first move (it surprised the hell out of a lot of people lol)