Spark Harvest

The additional cost is the whole pricing model: this is either a one-mana kill spell or a five-mana one, and which it is depends entirely on what you're willing to feed it. Black has always paid for unconditional removal somehow (a life payment, a double-color tax, a graveyard requirement), but this design pays with a body instead, and that changes the math for the deck built around it. In a sacrifice shell, the creature clause isn't a tax at all: it's a second trigger, converting a creature you were already going to throw away into removal that also answers planeswalkers. The escape hatch keeps the card castable when the board is empty, ensuring it never sits dead, but the five-mana price on that mode signals which half the design actually wants you to use. Compare it to the strict one-drop kill spells that demand a life payment or a graveyard cost up front: those ask "can you afford this?" This one asks "what are you sacrificing to cast it?" and for a deck built on death triggers the answer is usually "something I wanted gone anyway." The steep alternative cost is doing the balancing work, ensuring the discount only materializes when you've already committed to a board plan that generates expendable bodies. It is removal that reads its own deck before it reads the opponent's.