Genju of the Fens

The recursion clause is the entire point. A one-mana Aura that turns a Swamp into a 2/2 is unremarkable on rate; what holds the design up is that the land it depends on doubles as its weakness, and the card solves that weakness itself. A normal animation enchantment dies with its host, so killing the creature mode costs you both the land and the Aura at once. Here the land is expendable: lose the Swamp and the death trigger lets you recur this card, redrawing the attacker so the whole exchange collapses into trading a basic for the opponent's removal. Most turns it just sits as a Swamp, blanking sorcery-speed sweepers, and the pump runs on black mana, so a glut of lands converts into reach instead of dead draws. The five-Genju cycle each animated a basic with this same return-on-death loop, but black's is the one built for the long grind, where the land-for-removal swap is exactly the attrition a resource-conscious deck wants to force. It occupies a noncreature spell slot to include, yet an opponent who kills the animated Swamp only feeds the return; to answer it permanently they must destroy the Aura itself or otherwise avoid sending the Swamp to the graveyard. A recurring attacker for the kind of fight decided by who runs out of cards first.