Furtive Courier is a uncommon Creature — Merfolk Advisor card from Murders at Karlov Manor (MKM), collector number 59. Current market price: $0.10 (foil $0.04), TCGplayer market prices via Scryfall.
This creature can't be blocked as long as you've sacrificed an artifact this turn. Whenever this creature attacks, draw a card, then discard a card.