Karai's Technique is a uncommon Sorcery card from Teenage Mutant Ninja Turtles (TMT), collector number 152. Current market price: $0.18 (foil $0.23), TCGplayer market prices via Scryfall.
Sneak {W}{B} (You may cast this spell for {W}{B} if you also return an unblocked attacker you control to hand during the declare blockers step.) Choose one or both — • Target creature gets +3/+3 until end of turn. • Target creature gets -3/-3 until end of turn.