"A demonic pact is all fun and games until the bill comes due."
—Liliana Vess

Blasphemous Edict

You may pay {B} rather than pay this spell's mana cost if there are thirteen or more creatures on the battlefield.
Each player sacrifices thirteen creatures of their choice.

Foundations Promos

Foundations

If a player controls fewer than thirteen creatures when Blasphemous Edict resolves, they will sacrifice all of their creatures.

Starting with the player whose turn it is, each player in turn order chooses which creatures they will sacrifice, then all the creatures chosen by all players are sacrificed at the same time. Players get to know the choices made by players who chose before them.