If you could add a Pokemon type, what would it be?

We all know (or most of use know) that Pokémon X and Y will bring about the existence of a new type, the Fairy type. However, if you could add another type to the game, what would it be, and why?

The ideal answer should be like this:

Pokémon type: (...)
Reason for Type: (...)
Pokémon who would have type: (...)

If there are no real Pokémon who fit your type, then that is fine.

Chemical Type
Because there needs to be another counterpart of Poison, not all chemicals are relevant to battle because they're poisonous, some are relevant because they're corrosive.
Muk and Grimer would be given the type in addition to Poison, A branch evolution of Kadabra would be holding a beaker in the place of the second spoon and be a Psychic/Chemical type. 

Also the moves Acid, Gastro Acid, and Acid Spray would be changed to a Chemical type move, but there would obviously be new moves added to be Chemical type.

it would resist water, and steel would be weak to it. it would be weak to fire and rock would resist it. Rock needs an edge over Steel and all of that makes sense anyway. Also it could have other type effeciveness, I just don't feel like flavoring everything about it atm.

Truck ideal answers they're for punk mothah truckahs!