Shub-Niggurath, All-Mother

Stirs in It's slumber — Whenever two or more creatures controlled by a single player die, if
Shub-Niggurath, All-Mother is in the command
zone, that player gets a madness counter.
When Shub-Niggurath, All-Mother enters the battlefield, exile all other creatures, then each
player creates a black Horror Assassin creature
token with "Whenever this creature deals combat damage to a player, that player loses the game"
for each madness counter they have.