Crater Hellion

A board wipe stapled to a 6/6, with a rental agreement attached that makes the math sting before it pays off. Six mana lands the body and clears everything that fits under four toughness; the Hellion shrugs off its own pulse because the sweep deals four to each other creature, and a 6/6 was never in danger from four. Then echo arrives at the beginning of your next upkeep and asks for the full again, so the card is rented, not bought, and the bill comes due before you ever reach combat: the creature is summoning-sick the turn it enters, so the echo trigger fires before it can attack. Either you pay six again to keep a fat blocker you have not yet swung with, or you sacrifice it having gotten only the four-damage burst on the way in. That structure is the design discipline doing the balancing. A repeatable 6/6 that wipes the board on a flicker would be absurd, so echo prices the second turn at the cost of the first, and the sacrifice clause lets a player content to trade one sweep for one card treat the whole thing as an overpriced sorcery that happened to leave a body for a single upkeep. Note what echo does not let you escape: blinking or reanimating the Hellion makes it a new object that came under your control since your last upkeep, so the echo trigger fires again on top of re-firing the four-damage burst. You buy a second sweep, not a free one.