Tears of Rage is a uncommon Instant card from Darksteel (DST), collector number 70. Current market price: $0.25 (foil $1.01), TCGplayer market prices via Scryfall.
Cast this spell only during the declare attackers step. Attacking creatures you control get +X/+0 until end of turn, where X is the number of attacking creatures. Sacrifice those creatures at the beginning of the next end step.