Thats pretty strange. I don't think its a hybrid. I think its 100% mallard. But, sort of like you see white labs, yellow labs, and red labs, I think this bird probably has some sort of disorder or mutation that has effected his pigmentation. The beak is mallard drake (full plume) so is the head.

The real kicker is the speculum on the wing. It should be blue and white in full plumage, but it looks more like the wing of a ringneck hen. I think he has the measles or something like that.