The Deceiver's Grasp is a relic found in The Darkness II. According to Johnny Powwel it's the "third most infamous glove of all time". It was created by The Brotherhood to protect their agents from the side effects of the Abysmal Maw; a mystical hand cannon that shoots pure hellfire at the cost of slowly consuming a persons soul. When coated in the blood of another person the glove transfers the cost to the usually very unwilling donor. That person is then codemned to Hell in place of the one using the Maw.
Johnny Powwel humorously calls the Glove a "danmation contraceptive" when he describes the glove in-game.
Interestingly, even though the Abysmal Maw was to be used by the wielder's right hand, The Deceiver's Grasp appears to be a glove for the left hand.