Mutant Mayhem mixes heroes and villains from different times, dimensions, and worlds across the Marvel universe. The set includes 97 characters, including the debuts of teams like the Reavers, the Marauders, and Alpha Flight. Mutant Mayhem also introduces three new HeroClix game pieces: feat cards, which convey additional powers and abilities; battlefield condition cards, which affect the environment in which figures fight; and bystander tokens, which feature some of the most popular supporting characters in the Marvel universe.

With Mutant Mayhem, players also have the opportunity to find ultra-rare, one-of-a-kind Master Piece Spider-Man figures, each hand painted in exceptional detail. Each Master Piece figure comes complete with a certificate of authenticity. The set also includes the highly anticipated, oversized Giant Man super-rare figure.