Disciple of Phenax is a common Creature — Human Cleric card from Theros (THS), collector number 84. Current market price: $0.08 (foil $0.18), TCGplayer market prices via Scryfall.
When this creature enters, target player reveals a number of cards from their hand equal to your devotion to black. You choose one of them. That player discards that card. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)