Erratic Mutation is a common Instant card from Planar Chaos (PLC), collector number 41. Current market price: $0.05 (foil $0.40), TCGplayer market prices via Scryfall.
Choose target creature. Reveal cards from the top of your library until you reveal a nonland card. That creature gets +X/-X until end of turn, where X is that card's mana value. Put all cards revealed this way on the bottom of your library in any order.