Side-scrolling action platformer where you pick between two playable characters—Mega Man or Bass—each with distinct abilities. Mega Man charges his buster and slides; Bass rapid-fires and double-jumps but can't shoot while moving. You tackle eight Robot Master stages in any order, claim their weapons, then push through Wily's fortress toward a rogue robot named King who's hijacked Wily's castle and built an army from stolen blueprints. King believes robots should rule humans, forcing Wily and Light into an uneasy alliance. Stage design leans harder into verticality than earlier entries, especially for Bass's jump kit. Proto Man shows up, gets bisected by King's axe, then sits out repairs. No lives system—you retry from checkpoints. Originally Japan-only on Super Famicom in 1998; the later GBA port brought it worldwide with minor tweaks.
