Arcane Bombardment

The exile pool is the real payload, and it never shrinks. Each turn you cast your first instant or sorcery, the enchantment banishes one more spell from your graveyard into its own permanent stash, then copies every card that stash has ever collected. Turn one of its life you get a single free copy; three turns later you are casting free copies of all four exiled cards at once, and the trajectory only steepens as long as the enchantment survives. That compounding is what makes it a snowball rather than a repeatable value spell. The randomness is the tax on the ceiling: you cannot dig for the specific card you want, so the deckbuilding discipline is to make the whole graveyard worth exiling rather than seeding it with one bomb and a pile of chaff. A free copy of a burn spell is fine; a free copy of something that draws a fistful of cards or deals a table's worth of damage is a turn that ends games, and once it is in the pool it fires again every subsequent turn. Note the trigger cares only about your first spell each turn, so it is not itself a storm engine; it wants one deliberate cast, then reruns its entire history on top of it. That timing rewards decks already built to spend a turn resolving one large spell, letting the growing free cascade be the reward for surviving rather than the payload of a combo the enchantment powers alone.