An example would be fetch counters, used to mark cards exiled by [c]Haldan, Avid Arcanist[/c], and [c]Pako, Arcane Retriever[/c]
Not to mention that Little John, Resourceful Outlaw needing to be exerted to have his effect take hold is an easy cost to pay, considering how many resistant Bodyguards your opponents will likely have to get through to challenge him.
IIRC in Yugioh there is only a certain number of Blue-Eyes (from the show?), so you could put a rule on the card 'there may only be X Blue-Eyes on the battlefield at any time', Star Wars CCG used to have permanents that you could have 2 or 3 copies of in play, in addition to stuff you could only have 1 of, the concept would work fine here too, only this could care about both players' boards
Particularly, women with realistic body types