Crypt Rats

A repeatable Pestilence stapled to a body, and the body is what reshapes everything around it. Pestilence pays nothing but mana and ticks away on a clock; this puts the same X-for-X-damage engine on a creature, which means it can be tutored with creature searchers, returned from the graveyard, and rebought in ways the enchantment never could. The "spend only black mana on X" clause keeps the effect honest: it scales with how heavily you commit to black sources, not with raw ramp, so a deck full of off-color rocks gets no leverage out of it. The symmetry is the other half, and it cuts sharper here than on Pestilence. The damage hits every creature and every player, the Rat included, and on a 1/1 body even X=1 kills it. So this is not an incremental drain that ticks a wide board down over several turns; it is a one-shot button. You commit the black, you press it, and the card sweeps small creatures, burns each opponent, and usually dies to its own activation. That fragility is the access fee. It is what makes a board-wide damage source something black can fetch, sacrifice for a death trigger, and recur from the yard, turning a sweeper into a creature you can plan a graveyard around rather than a spell you cast once and lose.