Chittering Harvester is a uncommon Creature — Nightmare card from Ikoria: Lair of Behemoths (IKO), collector number 288. Current market price: $0.21 (foil $0.36), TCGplayer market prices via Scryfall.
Mutate {4}{B} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, each opponent sacrifices a creature of their choice.