Splinter Twin

The whole engine is a two-step tap dance: the aura grants its host a tap ability that mints a hasty copy, and if that copy can untap the original on its way to the battlefield, then a single creature with a self-resetting untap turns the activation into an arbitrary loop. Tap to copy, the copy untaps the host, tap again, and the board fills with hasty attackers until the end-step clause exiles every token. Splinter Twin is dead on its own; it needs a partner whose ability resets its tap state for free. Deceiver Exarch and Pestermite both untap a target as they enter, so attaching the aura to one of them and then activating the granted ability produces an unbounded swarm of haste-bearing copies. Both halves read as reasonable cards to draw alone: an untapping body that stalls the ground or taps down a blocker, and an aura that only becomes lethal once it lands on a creature whose own ability resets the tap (on anything else it just mints one temporary token a turn). The combo's resilience came from deploying the creature half at instant speed (often on the opponent's end step) and saving the sorcery-speed aura for the kill turn. The exile clause is the leash: every token vanishes at end of turn, so the engine yields nothing permanent unless the alpha strike ends the game, which is exactly what it was built to do.