Infernal Denizen

Control Magic stapled to a 5/7 body, with an upkeep cost engineered to bury you. Steal any creature with the tap ability and it stays yours as long as the Denizen survives, but the maintenance clause is where the design earns its scare. Every upkeep demands two Swamps off the top, and the moment you can't pay, the card inverts: it taps down and lets an opponent take their pick of your creatures, presumably including whatever you just stole. The threat ceiling is unbounded; the floor is a self-feeding land destruction effect aimed squarely at its own controller. That tension is what makes the design honest. Its era priced large creatures by their cost in cards and resources, not just mana, and few cards externalized that price as literally as this one: it physically eats your own board to keep working. The eight-mana sticker is almost beside the point. What kills the Denizen is the arithmetic of a finite Swamp count meeting an endless upkeep, a clock that ticks every upkeep whether the steal mattered or not. Wizards trusted symmetry-breaking effects of this vintage to police themselves through brutal upkeep taxes rather than through restrictions on what they could target, and the Denizen is that philosophy at its most punishing: a theft engine that will eventually rob you blind.