Formless

The Formless are the army of the Skeleton King and are the main antagonists during the first season of the show. They do not speak or have any expression, they're basically zombies made out of ooze that the Skeleton King commands at his will on his ship, the Citadel of Bone. On the ship he keeps a tank of ooze that makes his army to which to send to Shuggazoom to attack it. The Formless are very stupid and not very powerful, but when a large group of them come together, they can make a giant formless monster to attack the city. When a formless is defeated it will melt back into ooze. The formless are seen usually riding on motorcycles into the city.