Berserk is a uncommon Instant card from 30th Anniversary Edition (30A), collector number 181. Current market price: $17.78, 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.