Sorcerous Squall

If the 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 an instant or sorcery spell, you do so as part of the resolution of Sorcerous Squall. You can't wait to cast one later in the turn. Timing restrictions based on a spell's type are ignored.

If you cast a spell "without paying its mana cost", you can't pay any alternative costs. You can, however, pay additional costs. If the spell has any mandatory additional costs, those must be paid to cast the card.