"Knowing everything reveals not answers, but in fact their profound absence."
—Gadwick, the Wizened

Omniscience

You may cast spells from your hand without paying their mana costs.

Foundations

"The things I once imagined would be my greatest achievements were only the first steps toward a future I can only begin to fathom."
—Jace Beleren

Foundations Promos

If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

If you cast a spell "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, those must be paid to cast the spell.

Once you cast Omniscience, if it's your turn, you'll have priority immediately after it resolves. You can cast another spell before any player can attempt to remove Omniscience with spells or abilities.

You must follow the normal timing permissions and restrictions of each spell you cast.