Hexplate Wallbreaker

Extra combat steps have always come with a tax that keeps them fair: Aggravated Assault costs mana to reactivate, Combat Celebrant exerts and stays home the next turn, Relentless Assault is a one-shot sorcery. This one folds the enabler into a piece of Equipment that arrives with its own bearer already attached, which changes the math. The For Mirrodin! trigger means no separate creature is needed to carry it: it enters, makes a 2/2 Rebel, and suits that token up, so a five-mana investment lands as a 4/4 that untaps your attacking creatures and grants a second combat phase. The condition on the trigger (only during the first combat phase of the turn) is what stops the loop from running forever: each additional combat is not itself a first combat, so a single copy cannot re-trigger off the phases it creates. Attack with two equipped creatures in that opening combat, though, and both triggers see a first combat phase and both add a phase, so multiple copies still stack extra combats. What is structurally notable is how it collapses two roles that usually sit in separate cards. The extra-combat enabler and the threat it enables ride on one object, so the effect survives creature-based sweepers as long as the Equipment does, and it can be re-equipped onto something bigger for the Equip fee. It reads like a finisher for a wide board, but the token-plus-untap package also makes it a self-contained engine that asks little of the rest of the deck.