Phyrexian Monitor

Regeneration on a body this expensive was the kind of effect Wizards used to staple to creatures that didn't otherwise justify their cost, and this Skeleton is the limiting case: a 2/2 whose entire pitch is that it never stays dead. The activation costs only a single black mana, so as long as you hold a swamp open it shrugs off most combat and burn, blocks indefinitely, and keeps a regenerating wall in front of you turn after turn. The design lineage runs back through Drudge Skeletons and every other black wall-of-bones that traded offense for permanence, and the math is the same now as it was then: a creature that survives doesn't have to be good, it just has to be persistent and cheap to revive. What the body lacks is reach. Regeneration does nothing against exile, sacrifice effects, or being bounced, and a 2/2 that can only ever trade up by attrition is a clock that barely ticks. The card is built to outlast, not to win, which puts a ceiling on it that the rate alone can't lift; the recurring mana tax of holding black up to keep it alive is the real cost, paid every turn the creature matters.