Creeper

Creepers are purple ghosts who are always smiling in which they first appear in Luigi's Mansion: Dark Moon, they are first encountered at the Haunted Towers. They have infinite health and can only be defeated by using charged suction from the Poltergust 5000.

Abilities
Creepers have the ability to take the form of a puddle, the color of the puddle is purple, when Luigi steps over the puddle, he will be trapped inside the Creeper and will take continuous damage until he breaks free, creepers can also break into smaller forms.

Trivia
Creepers are spawned from a special varity of Gobber called the Creeper Launcher.

Creepers do not have a stronger form unlike other ghosts because they were not in the Crystal Mine.

An enemy in a popular computer game called Minecraft is also called a Creeper, but they do not look the same.