How about a Mario and Luigi game (like Superstar Saga, Partners in Time, Bowser's Inside Story, etc.) with other famous Nintendo bosses! You can also use bosses from the Mario games too! Being able to play as other Nintendo heroes is fine, and even encouraged, if you can find a way to use them in the battle system for M&L! (Note: You'll have to make your own sprites or import them.)
Current Boss List:
Kraid: Metroid Zero Mission
GUILT (Stigma is also fine): Trauma Center
Star Wolf: Star Fox
Bowser (Dark Bowser is okay too): Mario and Luigi: Bowser's Inside Story
SA-X: Metroid Fusion
Fawful: Mario and Luigi: Bowser's Inside Story
Ridley: Metroid Zero Mission
Ganondorf: Legend of Zelda: Twilight Princess
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