Mickey Mouse and the Army of Assists

[Kenpachi Zaraki]

First, I wanna say that I love this idea. It seems like it will yield some really excellent writing material. I think you've got a solid start.

Coruscant: Stitch is perfect for Coruscant (unless you wanted to do a Star Wars one since Disney acquired them) and I imagine him as an offensive option since he's noted for his enormous strength; maybe he'd be sort've a bruiser/pure damage build? I imagine him throwing cars. =P

Green: I'd probably go with Tarzan, personally. Maybe an assist based on tech and speed as he is known for being nimble? Or perhaps Tinkerbell? That could be a stretch, but I figured since Neverland is on a forested island I'd mention it. Could also be in the Deep?

Dunes: 100% agree with Genie. 'Nuff said.

Deep: As mentioned above you could add in Tinkerbell maybe. I'd kinda like to see King Triton, though. He'd be pretty cool for offensive/support, maybe summoning a giant squid to immobilize foes or casting huge waves to stagger them. Also, maybe Jack Sparrow?

Moores: Jack Skellington would be a badass option for this area. Maybe some necromagic, summoning chains Spawn-style or a bone-wall for defense?

Steppes: I'd have Mushu in the Ashen Steppes since the Ninja village is only a small part of the Tangled and being a dragon he seems to fit better in a more fire-based area (at least to me).

Frozen Fields: This one is probably the toughest. If you're avoiding Frozen, I can only think of Frozone from The Incredibles.

Edit: As for a flight form, I think the Magic Carpet is the perfect choice, unless you wanted to use a Fantasia-styled magic broom or something.