Yellow Devil

Yellow Devil (イエローデビル), also know as Rock Monster, is one of Dr. Wily's creations, that originally was a fortress boss in Mega Man 1 as a big yellow blob made of nanobots, that can dismantle himself and cross through the screen to attack enemies. His weak point is his eye, which is the controller of the nanobots. He can also shoot beams from his eye in the Mega Man: The Power Battle games.

In Mega Man: Powered Up, it is revealed that he can talk, but the only thing he can say is "Bumo".

A upgraded version of him appeared in Mega Man 3, called Yellow Devil Mark2. Mark2 can not only do the "blocks moving thing", but can also flow in a wave.

Yellow Devil also appear as a boss in the arcade games Mega Man: The Power Battle and Mega Man 2: The Power Fighters, and is a racer in Mega Man: Battle and Chase, along a secret boss recolor called Black Yellow Devil, shortened to Black Devil, which caused confusion between it and the Shadow Devil.

He reappeared in several other games in different forms, like: Mega Man 8 and Mega Man and Bass, as Green Devil, Mega Man V as Dark Moon, Super Adventure Rockman as New Yellow Devil, and in Mega Man 9 as Twin Devil. He also appeared in the X series in Mega Man X5 as Shadow Devil, including the Fortress Boss music and all! In Mega Man ZX, he appeared as a miniboss (except made out of magma instead of nanobots), named Lava Demon.