The Pale Skeleton Shirt represents a Skeleton Rib-Cage, and appears to come in many different colors, in which this one is Pale.
Pale Skeleton Shirt(s) are clothing items worn on your Body. Their rarity is Rare. You must be level 1 or higher to wear them. They are Unbound. Their origin is Crossroads. They are a Limited Edition item only available in the month of October. (Monkey Quest calls it OOK-tober!) You find them in Papa Matu's Haunted Graveyard (By smashing Pumpkins.) Below is a list of attributes they give your monkey.