Silent-Blade Oni is a rare Creature — Demon Ninja card from Planechase Anthology (PCA), collector number 105. Current market price: $6.19, TCGplayer market prices via Scryfall.
Ninjutsu {4}{U}{B} ({4}{U}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.) Whenever this creature deals combat damage to a player, look at that player's hand. You may cast a spell from among those cards without paying its mana cost.