Conjurer's Closet

Most enters-the-battlefield triggers honor a one-time contract: a single Mulldrifter draws two, a single Flametongue Kavu burns one thing, and that is the deal. This artifact rewrites the terms by handing you a blink at the beginning of your end step, once per turn, turning any creature with an entry effect into a slow, inevitable engine. Anchoring the trigger to your end step matters more than the colorless cost suggests: a creature exiled there returns with summoning sickness functionally irrelevant (it untaps before your next combat, ready to attack), counters and Auras fall away, and the fresh copy gets any "as it enters" choice again. Because the effect lives on an artifact rather than a creature or a spell, it survives the board wipes that clear the payoffs it is blinking and resumes grinding the moment a new target hits the table. The five-mana price and the once-per-turn ceiling are what keep it from tipping over: this is a value accumulator, not a combo piece, asking you to build a board of recurring triggers rather than chain flickers at instant speed. It does structurally what Flickerwisp and Restoration Angel do as one-shots, converted into a permanent that taxes nothing and answers no clock. The closet is patient; it pays you for keeping good creatures alive through your own end step, turn after turn, until someone removes the artifact itself.