Bone Splinters

• WWizards of the Coast2022-09-09
  Official Ruling
  Once you begin to cast Bone Splinters, no player may take actions until you’re done. Notably, opponents can’t try to remove the creature you wish to sacrifice.
• WWizards of the Coast2022-09-09
  Official Ruling
  You must sacrifice exactly one creature to cast this spell; you can’t cast it without sacrificing a creature, and you can’t sacrifice additional creatures.

Rulings via Scryfall