PYROSPHERE
Probably the most memorable scene in all of Metroid: Other M comes when the strange little creature Samus has been spotting here and there around the bottle ship reaches the final stage of its evolution and turns out to be a clone of Ridley, who then attacks Samus and her friend Anthony in the middle of Pyrosphere.
This is likely the reason why Pyrosphere was chosen as the stage for SSB4, a big large platform for battling that the Ridley clone would show up on from time to time and attack the players. I would include a bit more dynamic action than the stage did, with more of the lava and the stage being knocked around, or even the lift function that similar platforms use when mini-boss fights take place in the game.
Possible theme: https://www.youtube.com/watch?v=9Q3j0J9P1m0
