Frost: I'd love to see that appearing out. There's still plenty of other types left even after this one, but this sounds something I'd love to see being done the most (until I hear better ideas.)
About the Ghost-stage, maybe there should be few furniture that float up like they're possessed by mean spirits of underworld and try to hit the players, but should they avoid them, they can pick it up and throw them at others. They move predictably though.
Those would be Dark, Bug, Steel and Dragon.
Funny, since there are 17 types, but all Stadiums feature normal, leaving 16 types, which is a number divisible by 4, resulting in 4 types for 4 different stadiums.
I envision the Dark-type as a dark looking forest with black fog that obscured the view, making it difficult (but not impossible) to see wherever the characters were. Could feature Zoroark for illusions similar to my Psychic type transformation ideas, as well as other Dark-types like Umbreon, Shiftry and Bisharp.
Other idea could be a stage with invisible traps, as Dark-types are known for their trickery.
The Steel-type could be themed on a factory, featuring gears that had four platforms attached and would rotate depending on the character's weight and such. (Remember those sets of four platforms from the Mario games that you had to use your weight to move forward? Same idea.)
Some Pokémon featured would be Klink and its evolutions as part of the whole gear mechanism, as well as other Steel-types like Steelix, Mawile and Aggron.
Bug would also be forest themed, featuring trees and grassy floor. On the trees there would be some beehives, where honey could fall to the floor, becoming sticky and hard to move around. Between two trees, Spinarak or Joltik could make spiderwebs or electrowebs. The first would act as a bouncy platform that, if landed too much times, it would break. The other would be electrified and damage players who come on contact with it and, like normal webs, would end up being destroyed upon being in contact for too many times. Other featured Pokémon would be Combee and Beedril, obviously, as well as Butterfree, Venomoth and Volcarona, flying around the stage.
The Dragon type would be ruins themed, having several broken columns and featuring a large statue of a (rather generic looking) European dragon whose hands served as platforms. Several smaller Asian dragon statues would be facing the big statue. Sometimes, the big statue opens its mouth to breathe fire, damaging players who come in contact with it. Pokémon featured would be Dratini (in a small pond of water), Hydreigon (flying around the stage), Gabite and Druddigon.
