Gnawing Crescendo is a common Instant card from Wilds of Eldraine (WOE), collector number 131. Current market price: $0.24 (foil $0.22), TCGplayer market prices via Scryfall.
Creatures you control get +2/+0 until end of turn. Whenever a nontoken creature you control dies this turn, create a 1/1 black Rat creature token with "This token can't block."