 The mode begins as Mario and Kirby face each other on a stadium located in the Smash Bros. world. In this world, when a fighter is defeated, they turn into a trophy form, which can be revived by touching the base. Suddenly, smoke pours from the sky and the Battleship Halberd flies over. It releases a stream of black purple-clouded bugs called Shadow Bugs that form the soldiers of the Subspace Army. The Ancient Minister, a cloak-clad, mysterious hovering General of the Subspace Army, arrives with his Army and detonates a Subspace Bomb, which can only be detonated by the sacrifice of two R.O.B.s, and which transports the stadium into Subspace, an alternate dimension where the Subspace Army resides. The Ancient Minister's advance prompts the heroes to progressively team up and attempt to repel the enemy, while villains harvest the power of the allied characters by using dark cannons to convert them into trophies, and using shadow bugs on some of them to fight the protagonists during their adventure.
