Mazer is set on Earth, where an alien race called the Semag-Resal has taken control. They have built bases all over the planet and created cyborgs that can mimic humans to spy on the rebels and eliminate them. The player must choose a soldier to free humanity from this oppression.
The gameplay in Mazer is similar to Project Overkill, with an isometric view and a main goal of eliminating alien life forms in the bases and freeing human captives for bonuses. As the player progresses, the enemies become more difficult to defeat, culminating in a final boss: a giant alien robot.