Splinter's Technique is a rare Sorcery card from Teenage Mutant Ninja Turtles (TMT), collector number 233. Current market price: $2.29 (foil $2.61), TCGplayer market prices via Scryfall.
Sneak {1}{B} (You may cast this spell for {1}{B} if you also return an unblocked attacker you control to hand during the declare blockers step.) Search your library for a card, put that card into your hand, then shuffle.