Omniscience | Magic: The Gathering
Formats Omniscience is Legal in
Official Oracle Text for Omniscience
Official Rulings for Omniscience
7/1/2012 : If you cast a card "without paying its mana cost," you can't pay any alternative costs. You can pay additional costs such as kicker costs. If the card has mandatory additional costs, you must pay those.
7/1/2012 : If the card has X in its mana cost, you must choose 0 as its value.