Marx

Marx is a jester who first appears in the Kirby Super Star main game, Milky Way Wishes, serving as the main antagonist and final boss. His boss battle theme is Vs. Marx. Since his debut, Marx has made a cameo appearance in a few Kirby games, but has made two notable appearances: as a Dream Friend in Kirby Star Allies (since update 2.0.0) and as a boss in Super Smash Bros. Ultimate.

Marx has a round, lavender body, and he wears a jester hat, a bow tie, and brown shoes. Marx does not have any arms. He is frequently seen bouncing on a ball.

Super Smash Bros. Ultimate
In Super Smash Bros. Ultimate, Marx is the final enemy in the Classic Mode runs of Kirby, Rosalina & Luma, and Inkling. Sephiroth also fights Marx in his Classic Mode route, but not as a final boss. He also appears as a boss in the adventure mode, World of Light, where he serves under Dharkon. A Mii hat based on Marx exists in Super Smash Bros. Ultimate, unlockable for 450 G, that Mii Fighters can don.

The Vs. Marx theme is featured in Marx's boss battle (except for in the Classic Mode runs of Rosalina & Luma and Inkling).

Trivia

 * Tabuu, the final boss of Adventure Mode: The Subspace Emissary in Super Smash Bros. Brawl, uses similar moves to Marx.