Absalom

Absalom is an invisible being of some sort that kept five of the Straw Hats, Luffy, Zoro, Sanji, Robin, and Franky, from going ashore to the island. It later attacked Nami while she was bathing in the bathroom in Hogback's mansion. It apparently escaped out the window just as Usopp fired at it. It is currently unknown if he is a ghost or something else.