Shielded Aether Thief

A defensive wall that pays you to do its job, then turns the payment into cards. The 0/4 body invites attacks it survives, and the energy mechanic closes the loop: each block banks fuel, and three of those counters convert into a fresh card. Flash is what sharpens the whole thing. Hold up two mana and you can ambush an attacker after declare-attackers, dropping the Thief in front of a swing the opponent already committed to and banking energy off a block they thought was safe. The activation taps the Thief and costs three energy, which means it cannot recur indefinitely on the same fuel, but the timing is more forgiving than it looks: you can declare it as a blocker, let the energy trigger resolve, and still tap it to draw during the declare-blockers step without pulling it out of combat. The discipline is the energy threshold rather than any tapping restriction. You stockpile counters across several combats before the engine pays out, so a single block does not immediately bury an aggressor. That delay is the reason a two-mana repeatable card-draw engine can sit in front of a board with nothing better to do than throw bodies at it without warping the game. As a structural idea it sits among the energy payoffs of its era, but few of them tied the resource so cleanly to the act of blocking itself.