Predators' Hour is a rare Sorcery card from Crimson Vow Commander (VOC), collector number 21. Current market price: $0.32, TCGplayer market prices via Scryfall.
Until end of turn, creatures you control gain menace and "Whenever this creature deals combat damage to a player, exile the top card of that player's library face down. You may look at and play that card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell."