For unlimited flying power with Storm and Rogue, start a level with either of them. Turn on Mutant Power and jump up to fly. When you are in the air, tap and hold the ATTACK button, then tap START to turn off Mutant Power. The meter should turn off, but you are still in the air. You can stay up as long as you want until you touch ground.
At Avalon, the final stage, use Nightcrawler to teleport. Circumventing the left-most walls takes you directly to Magneto. When Nightcrawler becomes weary from battle, teleport through the opposite walls to Magneto's lair (a room filled with power-ups) before venturing back into the fray.
