An alien menace has attacked the worlds of civilization and laid waste to their planets. However, before being conquered, a group of scientists has managed to create one last weapon and hide it underground. The name of the weapon is Mag Max and only it might be able to defeat the alien invaders. Mag Max however is incomplete and for security reasons, his component parts are scattered across the land. Through their collection, Mag Max's strength increases.

Mag Max is a side-scrolling shooter game. At the beginning, Mag Max is only a tiny little fighter craft that can fire low-powered projectiles. As component pieces (such as a head, legs and a laser lance) are found, Mag Max's offensive power increases. The underworld can be accessed through small dark craters on the landscape. Once in the underworld, Mag Max's weapons vary slightly as do the enemies (there are no stationary objects underground). Enemy fire or contact on each of the components will destroy that component. Fire on the main fighter will destroy Mag Max. At the end of each level awaits a boss creature.