This is a one-of-a-kind "Sinister" silicone mask from Shattered FX.
This mask is cast from the second version mold of the "Sinister" mask. Custom paint, wig, and hand-punched widow's peak, made to look like The Joker as drawn/painted by Dave McKean in the classic 1989 graphic novel, "Arkham Asvlum: A Serious House on Serious Earth". Practically brand new, and just tried on.