
Legendary Enchantment
When The Meathook Massacre enters, each creature gets -X/-X until end of turn.
Whenever a creature you control dies, each opponent loses 1 life.
Whenever a creature an opponent controls dies, you gain 1 life.

Scalable black board wipe via -X/-X like Meathook.

Black sweeper destroying all creatures.

Flexible black wrath destroying all or non-dragons.

Cheap black mass destruction effect.

Scalable -X/-X wipe that reshuffles.

Gives all creatures -4/-4, similar one-sided potential.

Cascading -1/-1 board wipe in black.

Scalable black/green wipe destroying permanents.
If The Meathook Massacre enters the battlefield and it wasn't cast (or it was cast without paying its mana cost), X will be 0. The first ability will trigger, but it won't be much of a massacre.