Pulse of the Forge is a rare Instant card from Darksteel (DST), collector number 66. Current market price: $0.57 (foil $2.72), TCGplayer market prices via Scryfall.
Pulse of the Forge deals 4 damage to target player or planeswalker. Then if that player or that planeswalker's controller has more life than you, return Pulse of the Forge to its owner's hand.