Fire/Poison
I understand that a lot of peopl are interpetting this concept as demanding the worst type possible, but that's not nessacarily true. If we give it Ice/Rock, then we've all but decided what kind of mon it will be. Fire/Poison is still bad, but good enough that we can play with multiple roles without having to resort to massive movepool and stat buffs. Also, I feel artists will have more fun with this, and I'll have more fun looking at the concepts.