Marx made his debut in Kirby Super Star as the main antagonist. Kirby and his friends meet him at the beginning of Milky Way Wishes, and he asks if they can solve a conflict between the Sun and the Moon. Kirby and his friends agree, unaware that Marx is planning on using their aid for his own evil ends. Marx then steals their wish and makes a wish on the Galactic NOVA to control Kirby's home planet, transforming into his True form. Kirby then obtains the Starship ability and destroys the Galactic NOVA's heart, stopping his movement dead. The pink hero then fights and defeats Marx, sending him flying into the Galactic NOVA, their collision seemingly killing them both as their bodies appear explode upon impact.
In Super Smash Bros. Ultimate
In Ultimate, Marx appears as a boss at the end of Kirby, Rosalina & Luma, and Inkling's Classic Mode run, as well as in Adventure mode, as a servant of Dharkon. He resides in the Mysterious Dimension area. When the player answers the question about the Subspace Emissary correctly, Marx will appear in the center of the swirl and pull the fighter to his space. However, the player can leave this area and is not immediately forced to fight him.
In addition to his boss appearance, Marx’s regular form appears in the game as a spirit. When he is leveled up all the way, he becomes his True form.
Marx keeps most of his attacks from Super Star such as teleporting, shooting crescent blades, dropping an icy bomb, creating a black hole, and spitting out a massive laser beam. However, he has a new arsenal of attacks such as eye lasers and appendages that deal flame-type damage. The arrow attack is unused.
When entering Marx’s battle, it opens into an area reminiscent of Planet Pop Star, the area in which Marx is fought in Kirby Super Star. The screen turns to looking forward and no one is there. The camera then turns to look behind the fighter as they stop moving. Marx is just standing there. After a few seconds, Marx floats in the air and then transforms into his True Form, starting the battle.