Blood Oath is a rare Instant card from World Championship Decks 2001 (WC01), collector number jt177sb. Current market price: $0.45, TCGplayer market prices via Scryfall.
Choose a card type. Target opponent reveals their hand. Blood Oath deals 3 damage to that player for each card of the chosen type revealed this way. (Artifact, battle, creature, enchantment, instant, kindred, land, planeswalker, and sorcery are card types.)