Gun Mayhem 2 is a fighting game in which the goal of the player is to knock the opposing player off the edge of the map. The player controls the game by using the arrow keys for movement, the "Z" button to shoot and the "X" button to use a bomb.
Gun Mayhem 2 also allows multiplayer games on a single machine. The second player uses the "W," "A," "S" and "D" keys for movement, "T" to shoot, and "Y" to throw a bomb. The game also allows for a third and fourth player, but the users must program the controls themselves.
The game offers three different modes, "Campaign," "Custom Game" and "Challenges". In "Campaign," players fight against the artificial intelligence in a series of specific missions. Missions vary greatly and include scenarios in which the player fights against invisible opponents and opponents that are abnormally small. "Custom Games" allow the user to create their own scenario based on a variety of options such as "Last Man Standing" or "1 Hit 1 Kill". The "Challenges" section forces players to take on enemies while only using a specific type of gun, such as a SMG or a shotgun. Both the "Campaign" and "Custom Game" allow for co-op, while the "Challenges" must be tackled solo.