Mizzium Mortars is a rare Sorcery card from GRN Guild Kit (GK1), collector number 32. Current market price: $0.61, TCGplayer market prices via Scryfall.
Mizzium Mortars deals 4 damage to target creature you don't control. Overload {3}{R}{R}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")