Killer Instinct is a rare Enchantment card from Guildpact (GPT), collector number 120. Current market price: $0.30 (foil $1.14), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, reveal the top card of your library. If it's a creature card, put it onto the battlefield. That creature gains haste until end of turn. Sacrifice it at the beginning of the next end step.