The slaughter of his people by unliving monsters, . . .

Fleshbag Marauder

When Fleshbag Marauder enters, each player sacrifices a creature of their choice.

Grixis is a world where the only things found in abundance are death and decay. Corpses, whole or in part, are the standard currency among necromancers and demons.

Aetherdrift Commander

The List

Ravnica: Clue Edition

When Fleshbag Marauder enters the battlefield, each player sacrifices a creature.

Secret Lair Drop

As Fleshbag Marauder's ability resolves, first the player whose turn it is chooses a creature to sacrifice, then each other player in turn order does the same knowing the choices made before them. Then all those creatures are sacrificed simultaneously.

When its ability resolves, you may sacrifice Fleshbag Marauder itself. If you control no other creatures, you'll have to sacrifice Fleshbag Marauder.