Finale of Promise

A split card that's an instant and a sorcery card may be the target of Finale of Promise twice. However, once you cast that card once, it can't be cast a second time.

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

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 the spell has damage divided as it was cast, the division can't be changed (although the targets receiving that damage still can). The same is true of spells that distribute counters.