Proven Combatant

The pitch is one card, paid for at two different points in the game: a 1/1 you're happy to spend early, then a 4/4 you're happy to keep when six mana is sitting idle. Eternalize is the recursion variant that mints a fresh token instead of returning the original, and the design logic is to make the first cast feel almost free precisely because the second use is so expensive. The graveyard activation is steep and sorcery-locked, so this is never a flash threat or a combat surprise: it's a slow, inevitable body that asks you to commit the little creature for whatever a 1/1 can do, then bank on the late game to find the mana. What makes the structure clever is that the second life is generated, not recovered: exile removal aimed at the graveyard can strip it, but a wrath or a chump block on the original does nothing to the copy waiting offstage. That split, between a creature you're glad to trade and a creature you're glad to hold, is the entire appeal, compressed into a single blue Warrior that never sits dead in hand.