X-Men is a side-scrolling action game starring the mutant characters from Marvel's comic book series. Players start off with a choice of either Cyclops or Wolverine, and must progress through a variety of stages on their way to confront Magneto. Completing each stage unlocks an additional X-Men character, giving players more choices as they advance.
If one of the team members dies on a level, players lose that member, but can continue the game with the other X-Men available to them. The game ends when players have lost all their X-Men characters. Consequently, players start off with the equivalent of two lives in the game, and earn one more for each level completed.
The X-Men each have a health bar and a power bar. The health bar is diminished whenever the character takes damage from enemies, traps, or from falling, while the power bar decreases as characters use their special mutant powers. Players can replenish their characters' health bars by picking up hearts and their power bars by picking up X icons.
Each of the X-Men team members has his or her own special mutant power, ranging from claws to energy blasts. When activated, pressing the punch button uses the power. Powers can be activated or deactivated at any time in the game, although if a character's power bar is empty, that character cannot use his or her power.