The most similar effects in paper are cards like Kindle that need you to track the amount of Kindle cards in your graveyard, and cards like Yidaro, Wandering Monster that ask you to track how many times it was cycled
Even more surprising than that, however, is the fact this card, Nazgl, could take up five spots in this top ten list
Once its here, its here, so reprinting it at least drives the price down (perhaps only of the reprints, which Ben Bleiweiss is going to have to explain to me someday) so that everyone who wants it can get their hands on it
Instead, its Awaken the Blood Avatar thats really playable in those decks
Due to this, demand is likely going to fall off once players have had their fill