Creature — Horror
When Abyssal Gatekeeper dies, each player sacrifices a creature.
"There are two ways for me to pass this gate. One involves you remaining conscious."
—Gerrard of the Weatherlight
Legal in Legacy
Legal in Vintage
Legal in Commander
Legal in Pauper
The “sacrifice a creature” effect is not targeted. It can affect creatures with protection from black, for example.
The player whose turn it is chooses a creature to sacrifice, then each other player in turn order chooses a creature to sacrifice, then all chosen creatures are sacrificed at the same time.