The Devil Mask was an evil counterpart to the God Mask in Castlevania: Lords of Shadow.
The Devil Mask was worn by Zobek. It is possible that the Devil Mask was the source of Zobek's vast and terrible power and untold knowledge bestowed by Satan. Zobek used that mask on Gabriel Belmont in order for him to murder his wife, Marie, and his ally, Claudia; which took a big part on Gabriel's descent into darkness, turning him into Dracula. Before the ending credits, after Satan burned Zobek alive, it was lying on the ground behind Gabriel, indicating that Zobek had survived.