Rulings
You must sacrifice exactly one creature to cast Demon of Catastrophes; you can’t cast it without sacrificing a creature, and you can’t sacrifice additional creatures.
(wotc • 2018-07-13)
Players can respond only after Demon of Catastrophes has been cast and all its costs have been paid. No one can try to destroy the creature you sacrificed to prevent you from casting this spell.
(wotc • 2018-07-13)
Rulings
You must sacrifice exactly one creature to cast Demon of Catastrophes; you can’t cast it without sacrificing a creature, and you can’t sacrifice additional creatures.
(wotc • 2018-07-13)
Players can respond only after Demon of Catastrophes has been cast and all its costs have been paid. No one can try to destroy the creature you sacrificed to prevent you from casting this spell.
(wotc • 2018-07-13)