The peaceful planet Nibia is under attack from Vortex invasion armies. Attempts to contact the Guardian outpost of Arbor prove unsuccessful, so they have no choice but to surrender. There is one Guardian robot left, but because he is unstable he is kept into stasis, not even to be used in times of crisis like these. When an enemy missile destroys part of the cryogenic containment facility he is kept in however, he is freed and sets out to save the world and destroy his archenemy Absorbemon.
Explodemon! is a 2.5D action platformer in which the player controls the aforementioned, titular Guardian robot. Key element in the gameplay is that Explodemon is able to explode on command, and if left alone for long enough will do this automatically. This feature can be used to boost jumps, blow up enemies, sprint a short distance and solve physics-based puzzles. The power of an explosion depends on an energy bar which is also used to determine the health status, and can sometimes be refilled by killing enemies. Throughout the twelve levels, Explodemon will receive some new abilities like double-jumping and aiming. There is also an upgrade shop where the player can spend picked-up credits on stuff like better armor or more explosive power.