idk, book of moon thing maybe? I can't think of a reason off the top of my head why it's banned, but most of these are banned due to being wayayyy overusable and powered to the point where they screw up the yugioh economy (everyone gets one type of deck, causing loss of money etc). Think of some otk with it. if it's easy,that would be why XD.
but yeah, I don't know why. I'll check up on it.