From Board Game Geek:
Fluxx is a card game in which the cards themselves determine the current rules of the game. By playing cards, you change numerous aspects of the game: how to draw cards, how to play cards, and even how to win.
Marvel Fluxx features the gameplay of Fluxx and characters and events from the Marvel Universe.
Note that the Looney Labs edition of the game includes seven additional cards and a collector’s coin used in gameplay.