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When this creature enters, each player sacrifices a creature or planeswalker of their choice.
As the triggered ability resolves, first the player whose turn it is chooses a creature or planeswalker they control, then each other player in turn order does the same, knowing the choices made before them. Then all the chosen creatures and/or planeswalkers are sacrificed at the same time.
Demon's Disciple can be the creature sacrificed for its own ability.
