Berserk is a mythic Instant card from Secrets of Strixhaven Mystical Archive (SOA), collector number 50. Current market price: $6.74 (foil $8.70), TCGplayer market prices via Scryfall.
Cast this spell only before the combat damage step. Target creature gains trample and gets +X/+0 until end of turn, where X is its power. At the beginning of the next end step, destroy that creature if it attacked this turn.