Greaper

A Greaper is a ghost-like creature from the game Super Mario RPG: Legend of the Seven Stars. They appear in the Sunken Ship. These hooded ghouls resemble a cross between a Shy Guy and the Grim Reaper, hence their name. Greapers are related to the powerful Glum Reapers. One friendly Greaper is a member of the Three Musty Fears from Monstro Town. One specific Greaper also showed the ability to take the appearance of Mario, reflecting almost everything of the plumber's movements.

Trivia

 * Nintendo Power forgot to list Greaper's stats in the Super Mario RPG Nintendo Player's Guide. The reason they falsely gave was that Greaper wasn't an enemy in the game.
 * In the Japanese version of Mario & Luigi: Partners in Time, Boo Guy is given Greaper's name.