Arcane Bombardment is a mythic Enchantment card from Outlaws of Thunder Junction Commander (OTC), collector number 154. Current market price: $5.23, TCGplayer market prices via Scryfall.
Whenever you cast your first instant or sorcery spell each turn, exile an instant or sorcery card at random from your graveyard. Then copy each card exiled with this enchantment. You may cast any number of the copies without paying their mana costs.