The Mysterious Abyss (ワンダーオブアビス Wandā obu Abisu?, lit. "Wonder of Abyss") is a Keyblade acquired after defeating Ursula in Kingdom Hearts II and Kingdom Hearts II Final Mix. This Keyblade is the equivalent of the Crabclaw Keyblade from Kingdom Hearts.
The teeth and blade of the Keyblade are in the shape of a water spout. The token is in the shape of a white shell connected to the handle which is made up of assorted shells by a golden chain. In the center of the guard is a shell that has a small blue pearl in the middle.
This Keyblade's name probably refers to the mysterious wonders of the deep sea.