Just make a Joker out of it and make the mask an ancient death mask from an Aztec era culture where there's an actual ritual where they bound demons to a mask and wore them and were possessed by the demon in turn. Then transplant that into the modern day where some spineless forever alone corporate slave with a shitty life finds the mask just after his life falls apart (gets fired, etc.) and he puts it on and it makes him into a GTA character in real life with all the cheats activated where he can't be killed, has superpower, superspeed, can teleport etc. but don't make him into a real life cartoon as you want this to be halfway grounded, dark and "realistic".

what do you guys make of my pitch? will you front the shekels to make it?