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The neck of the Keyblade appears to be that of a skeletal dragon, of which still has life in some of it. Unlike most Keyblades, this Keyblade features a curved neck. The handle is the landmark that defines The Underworld and is seen on the river Styx. The token is the Hades Cup.
The Fatal Crest gives the largest magic bonus of any Keyblade, making it good for usage with Wisdom Form. Its usefulness for this is undercut by the Winner's Proof Keyblade in Kingdom Hearts II Final Mix, which boasts of slightly more powerful stats. Since the finishing move is disabled when this Keyblade is equipped, boss battles must be ended with a special attack, such as magic or a limit.
The Valor Form edition of the Play Arts Figures comes packaged with Fatal Crest as one of the Keyblades. Ironically, Fatal Crest is best used for its magical capabilities--and since Berserk Charge requires a complete loss of MP, Fatal Crest is essentially useless for Valor Form as the use of magic is sealed during this form.