Death Pits of Rath

A global rules-rewrite dressed as an enchantment: while it remains in play, the entire game's damage math collapses to a single threshold. Toughness stops being a buffer and becomes a binary. Any creature that takes a point of damage, from a Mountain's worth of burn or the smallest first-strike chip, dies, and the no-regeneration clause shuts the era's standard escape hatch so nothing crawls back. This is the design that turns deathtouch into the default state of combat: every blocker trades, every attacker that connects with a creature kills it, and a one-power swarm threatens as much as a board of dragons. The mirrored effect is both the lure and the liability; it punishes whoever has committed more bodies, so it rewards a controller who keeps the battlefield empty and lets the opponent walk into a death sentence. Where most black removal answers one threat at a time, this answers the concept of threats, converting any damage source you already run into a sweeper-on-tap. What holds it in check is its fragility and its blindness: it is an enchantment that can be removed, and it cannot tell your creatures from theirs, so building around it means leaning on reach, evasion, or board states the symmetry leaves intact. It belongs to a black design lineage the color has returned to ever since: change the rules, then exploit the asymmetry you engineered.