in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.Omniscience lets you cast spells from your hand without paying their mana costs, turning a stocked hand into an enormous potential turn. The enchantment costs ten mana to cast normally, so a blue deck needs either substantial acceleration or another way to put it onto the battlefield. Its payoff depends on having useful spells available after it resolves.
Draw spells keep the sequence moving by replacing the cards you cast for free. Enter the Infinite can provide an extreme payoff, while more ordinary draw engines can still turn Omniscience into several powerful spells in succession. In decks built around deploying enchantments through other effects, the ten-mana price can become a construction problem to solve rather than a cost paid every game.
The permission applies only to spells from your hand. Cards in the graveyard, exile, or on top of your library need their own casting permissions and payment arrangements. Normal timing rules also remain in place, so a creature or sorcery does not gain flash simply because its mana cost can be skipped.
Additional costs still matter, and a spell with X in its mana cost normally requires X to be zero when cast without paying that cost. Keep those restrictions in mind when choosing finishers. Omniscience is strongest when your deck can both establish it and immediately convert the resulting casting advantage into cards, protection, or a win, rather than leaving an expensive enchantment on an empty hand.
