The fourth edition in the GBA's Mega Man Zero sub-series finds the young hero continuing his efforts to forge peace between the humans and the reploids, in the futuristic world of Neo Arcadia. As he fights his way past the evil Dr Weil's dangerous minions, Zero can salvage equipment from defeated enemies and combine these parts to make his own custom weaponry. The game features a weather system, which can be altered by the player to raise or lower the game's difficulty. In all, the hero will face 40 different enemy types on 16 side-scrolling stages, each with a challenging, themed boss at the end.