I'll provide background I guess.
Marx was a jester thing that appeared in Kirby Superstar (and it's remake) as the final boss of the subgame Milky Way Wishes. In the first cutscene, he appeared to be an innocent puff ball thing not unlike Kirby who had no arms. He was always bouncing on a ball in said cuscene. He asks Kirby to go stop the sun and the moon from fighting (which he caused) by summoning the "comet" Nova. When this task is completed, before Kirby can wish for the sun and the moon to stop fighting, Marx drops out of nowhere, and wishes to take over the world. He then reveals his true form, and disappears. Once defeated, he flies into Nova, and blows up. However, in the remake Kirby Superstar Ultra, he is revealed to have survived, and appears in an even creepier form; Marx Soul, who appears as the Final Boss of the True Arena. When defeated, he has an earape scream. Marx has also has lots of cameos sense his first appearance.