Galaxy Defenders is a sci-fi cooperative, tactical battle game in which 1-5 players fight together against an oncoming alien menace. Each player takes control of one or more agents with unique powers to defend the planet from the alien invasion. Gameplay revolves around a tactical combat system, using custom ten-sided dice. Each player sequentially plays his Agent turn and then one Aliens turn. Players carry out their turns [agent and aliens] in clockwise order until the last player finishes his Aliens turn. Once done, the game passes to the Event phase that will bring the players to the next round. Players may choose up to five agents:

Marine: Coming from U.S. Special Forces, the Marine is an excellent soldier who can manage different combat situations, especially multiple enemies.

Biotech: The Biotech is the most technologically adept agent in service. He can use Nano-Technology to heal wounds or control war drones.

Infiltrator: A deadly and stealthy agent. This lethal specialist prefers hiding in the shadows. She has fast movement and good short-range combat ability.

Sniper: A silent sharpshooter and expert in camouflage and ranged combat. The sniper has average movement and excellent long-range firepower.

Hulk: The Hulk was a successful mercenary and now is one of the best agents; although slow, he enjoys an extraordinary resistance to damage and has high firepower.