Sharuum the Hegemon

The recursion clause reads like fair midrange value: rebuy a destroyed mana rock, a Solemn Simulacrum, a powerful equipment. But because she is herself an artifact creature, the ability that returns "any artifact card" from your graveyard hands you a loop the moment a copy of her is sitting there to grab. The famous line runs through a clone effect like Phyrexian Metamorph: copy Sharuum while one Sharuum is already in play, the legend rule sends one to the graveyard, and the survivor's enter trigger returns the dead copy. Each return retriggers the next, and the cycle only needs an Altar of Dementia or a Blood Artist attached to convert the infinite enter-and-die into a kill. Note the timing that makes this strict: targets are chosen when the enter trigger goes on the stack, so a freshly cast Sharuum is already on the battlefield and cannot point at herself. The loop genuinely requires the clone, which puts a copy in the yard via state-based actions before the trigger ever asks for a target. That she does all this on a 5/5 flier for six, in the precise three colors built to hoard artifacts, is what made her the default artifact commander for a generation of Esper builders: a printed ability that scans as modest recursion while the legend rule quietly supplies the win condition.