Claw of Abraxas is a unique two-handed sword. This weapon can be purchased from Mysus at the Black Market under Lanilor Lane in Aleroth during the events of Divinity II: Flames of Vengeance. To enter the Black Market you need to mindread Nerk, who is standing guard next to the Playhouse across the road from Madame Eve's. Claim to be Dormen and he'll unlock the trapdoor to the market.