Dragon's Fire is a common Instant card from Foundations Jumpstart (J25), collector number 134. Current market price: $0.27, TCGplayer market prices via Scryfall.
As an additional cost to cast this spell, you may reveal a Dragon card from your hand or choose a Dragon you control. Dragon's Fire deals 3 damage to target creature or planeswalker. If you revealed a Dragon card or chose a Dragon as you cast this spell, Dragon's Fire deals damage equal to the power of that card or creature instead.