When Will You Learn?

If the owner of one of the exiled cards leaves the game, that card leaves the game as well.

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

You must cast any of the exiled cards you wish to cast for free while this scheme's ability is resolving. You can't wait until later in the turn. Any cards not cast this way remain exiled for the rest of the game. The spells will be added to the stack in the order that you cast them.

Now you have learned.

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