It appears to be a fantasy variant scythe or bill, probably bone bladed, either a giant mandible or possibly a talon. Off hand I'd say it's a reach weapon, and good for tripping attacks. Damage wise I'd offer a 1-8 to 1-10, a x3 crit, and slashing damage. That thing doesn't look properly weighted to be a double weapon, and it's easily 13-15 pounds.