So one of the things that occurs to me is that, Greed Island is a game built in the real world by 11 Nen users, does that mean that those Nen users possess the Nen abilities of every card in the game? I mean, they'd have to have that ability to make a card that can do that ability wouldn't they? Especially since they can make the cards work in the real world if they want.

Either that, or it's one person whose Nen ability is that they can do anything, provided they have the ridiculous requirements that make up the entire game.