PURPLE

That's an easy one. Light type
good against: dark, dragon, bug
weak to: dark, psychic

I said crazy! not reasonable, but prolly a little too predictable.

im surprised they didnt add a light type in gen 6

light, cyber, cosmic, plastic, paper, glass, and pastry are what I can think of... a few of those are silly, but awesome silly! cupcake pokemon! x3

Anti-matter. =D
The pokémon with this type will create a black hole and suck in the trainer, thus fusing with them to become a half-pokémon half-trainer type. :3
(In short those pokémon would become a sort of empty shells of existing pokémon)

Silly <insert your species here>, antimatter doesn't make blackholes, it is the exact opposite of matter and when coming in contact with is causes the annhilation of both followed by the release of large amounts of energy. But that is an interesting thing to be a pokemon type.