Foul-Tongue Invocation is a uncommon Instant card from Dragons of Tarkir (DTK), collector number 102. Current market price: $0.15 (foil $0.31), TCGplayer market prices via Scryfall.
As an additional cost to cast this spell, you may reveal a Dragon card from your hand. Target player sacrifices a creature of their choice. If you revealed a Dragon card or controlled a Dragon as you cast this spell, you gain 4 life.