I think if we're going to bother adding new types, they should help balance out the completely broken weaknesses, strengths and resistances. How about:
Super Effective against: Dragon, Curse Not Very Effective Against: Ice, Poison, Ghost Weak to: Curse, Poison Resists: Dragon, Fighting
Basically, the uber powerful dragons have something to keep them in check a little. Ice gains a much needed resistance. And Poison gets the super effective hit it desperately needs.
Perhaps Curse wouldn't be the best type for it, but you have everything else right.
Air/Wind Type? Too similar to Flying(which already does have a few wind attacks- those would have to be reassigned and some new Flying moves would be needed)?
Storms can cancel out other storms, it works as an anti-dragon type. Colder weather tends to bring about less storms.(Ice Resist). Poison can represent pollution. Fighting would clearly not do much to the air...
I would love a light/holy type. I loved the concept of them in the card games.
They don't have to appear opposite of dark, they can represent themselves. The attacks would be based on light energy and magic. Yes it would be similar to other types, but not the same. Light energy isn't the same as electricity or sunlight. And it's not like the typechart makes sense as it is. Rock and ground are very similar. And so are Dark and Ghost. I also love the concept of angelic like pokemon, so I'd be happy. However, I'd only want it if it balanced the game out, otherwise it's quite unnecessary.
I support: Toad, Ridley, Palutena, Dixie, Shadow, Bowser Jr, Daisy, Little Mac, Mewtwo, Pichu, Krystal and Shantae for SSB4!
I like the idea of an Alien or Cosmic type. I'm not sure what its strengths and weaknesses would be, but a number of already-existing Psychic types can easily be retconned into Cosmic types without much incident. I'm thinking...
-Starmie -Unown -Lunatone -Solrock -Beldum line -Jirachi -Deoxys -Cresselia -Elgyem line
The Clefairy line also fits, and Sigilyph is another good candidate.
I claim to be the official Porygon2 of the Pokemon Black 2 board. Scientist MileRun: WaRy associate