Bayou Groff

• WWizards of the Coast2021-04-16
  Official Ruling
  Players can respond to Bayou Groff only after it’s been cast and all its costs have been paid. No one can try to destroy the creature you sacrificed to stop you from casting this spell or to make it cost more mana.
• WWizards of the Coast2021-04-16
  Official Ruling
  You must sacrifice exactly one creature or pay an extra to cast this spell; you can’t cast it without paying one of those costs, and you can’t pay either multiple times.

Rulings via Scryfall