Devastating Onslaught is a mythic Sorcery card from Edge of Eternities Promos (PEOE), collector number 132p. Current market price: $1.99 (foil $2.25), TCGplayer market prices via Scryfall.
Create X tokens that are copies of target artifact or creature you control. Those tokens gain haste until end of turn. Sacrifice them at the beginning of the next end step.