Dragonlord's Prerogative is a rare Instant card from Dragons of Tarkir (DTK), collector number 52. Current market price: $0.24 (foil $1.48), TCGplayer market prices via Scryfall.
As an additional cost to cast this spell, you may reveal a Dragon card from your hand. If you revealed a Dragon card or controlled a Dragon as you cast this spell, this spell can't be countered. Draw four cards.