New stages

[Zabi]

Especially I like the doomship and Advance Wars Stage. A new Starfox stage should probably be that Dinosaur planet (haven't played the game). Perhaps changing between two parts (ruins / jungle) like in Castle Siege in Brawl would be interesting.
I just throw my ideas of (not that creative) stages in:
Bowser's Castle (Mario series)
The thwomps could fly high and fall continually and serve as plattforms. When they fall on a character they cause damage and knockback similiar to Kirby's stone. The axe in the center appears from time to time. Hitting it causes the wooden plattform to fall down into the lava (but reappears after some time).
Twilight realm (Zelda series)
That would be quite a big stage. That cyan plattform on the right moves like in the game. Haven't thought of that much features, perhaps getting dark or shadow birds attacking the characters.
Mt. Dedede (Kirby series)
(I only know the Kirby Super Star (not Ultra) design, but that's not important.) A pretty basic stage. When you run into the ropes you will bounce back. Maybe you could put some characters who didn't make the cut or side characters in the audience.

I know, these are not the most creative and original stages, but I mostly thought of what stages would be cool to see in the game =]. I can come up with some more, if you guys want.