God so many choices... Gonna go with Sparkman! One of if not the favorite stage music and just... Really fun. Dunno how it'd work in ultimate tho...
Hmm...How about a stage that has two main platforms kinda like Reset Bomb Forest, but without the semi-solid platforms on the right, and the main platforms are bigger. There would be two chutes on either side of the stage that will release items, junk that hurt players, and those zappy enemies from the beginning of the stage. Also, on the far left and right are the rising platforms that sit near the bottom and can save players, but will rise up when stood on or grabbed, and will speed up at a quick pace. If they reach the blast zone, you will be K.O.'ed.
Either Magma Dragoon or Frost Walrus. I just... really like those guys. I suck at MegaMan games, though.
That said, Ice Man and Snake Man are cool. >.>;
The Spark Man concept was fun so I'll make one for some of your picks as well:
Volcano:
Three platforms suspended over lava that have two semi-solid platforms that fill in the gaps between them. Sometimes a fireball arcs around one of the platforms, or a few meteors rain down from the sky. Ride Armours will often spawn, and if players get in, they can walk around in the lava for a time.
Snow Base:
A stage with one main platform. This platform has walls going all the way down, and slants upward in the center, creating a raised surface. The stage is quite wide to compensate for the fact that it has ice physics, and that players will slide down the slants when they stand on them, which effectively splits the stage into three parts. Periodically, snow platforms will form on the sides of the stage as well as above the center. They appear long enough to be used strategically, then disappear again.
I was planning on doing Ice Man and Snake Man's stages, but I've exhausted my creativity for now.