Capsize

The clearest demonstration of buyback's whole design conceit: a spell that refuses to leave. Strip the keyword away and you have a slightly overcosted Boomerang, a one-shot tempo play. Pay the surcharge and that one-shot becomes an engine, because the spell comes back to your hand as it resolves. Every turn you untap, pick off a land, a creature, an artifact, anything, and the card waits in hand to do the same the following turn. The mana floor is the balance lever. Buyback refunds the spell, not the cost, so a repeatable cast demands a heavy commitment each turn, and what that commitment buys is bounce rather than removal: the permanent returns, it is never actually dealt with. That gap between "perpetual" and "permanent" is the entire design tension. Capsize does not win on its own; it locks. Point it at an opponent's only land and they never untap with mana again; chip their board apart piece by piece while a clock ticks elsewhere. It is the archetypal soft-lock tool, proof that you do not need to answer a problem once if you can answer it every single turn. Buyback as a mechanic was built to ask whether reusability was worth a premium; Capsize is the answer that showed how dangerous the question could get.