Any time you could cast a split card with fuse, you can choose one half and cast it, just like any other split card. If you're casting it from your hand, you have the additional option to cast both halves as a single spell by paying their combined cost. Instructions on the left half are processed first, then the instructions on the right, and targets for the two halves are chosen separately.
- If you’re casting a split card with fuse from any zone other than your hand, you can’t cast both halves. You’ll only be able to cast one half or the other.
- To cast a fused split spell, pay both of its mana costs. For example, Dirty (Down/Dirty) has mana costs of and . To cast both halves, you pay . While the spell is on the stack, its converted mana cost is 7.
- You can choose the same object as the target of each half of a fused split spell, if appropriate. For example, if both the left and right halves of a split card require a "target creature," you can choose the same creature for each instance of the word target (but you don’t have to).
- When resolving a fused split spell with multiple targets, treat it as you would any spell with multiple targets. If all targets are illegal when the spell tries to resolve, the spell is countered and none of its effects happen. If at least one target is still legal at that time, the spell resolves, but an illegal target can’t perform any actions or have any actions performed on it.
- When a fused split spell resolves, follow the instructions of the left half first, then the instructions on the right half.
- In every zone except the stack, split cards have two sets of characteristics and two converted mana costs. If anything needs information about a split card not on the stack, it will get two values. For example, if a player reveals Dirty (Down/Dirty) due to Duskmantle Seer’s ability ("At the beginning of your upkeep, each player reveals the top card of his or her library, loses life equal to that card’s converted mana cost, then puts it into his or her hand."), the game will see its converted mana cost as 4 and 3. This translates to that player losing a total of 7 life.
- On the stack, a split spell that hasn’t been fused has only that half’s characteristics and converted mana cost. The other half is treated as though it didn’t exist.
- Some split cards with fuse have two monocolor halves of different colors. If such a card is cast as a fused split spell, the resulting spell is multicolored. If only one half is cast, the spell is the color of that half. While not on the stack, such a card is multicolored.
- Some split cards with fuse have two halves that are both multicolored. That card is multicolored no matter which half is cast, or if both halves are cast. It’s also multicolored while not on the stack.
- If a player names a card, the player may name either half of a split card, but not both. A split card has the chosen name if one of its two names matches the chosen name. This is a recent rules change.
- If you cast a split card with fuse from your hand without paying its mana cost, you can choose to use its fuse ability and cast both halves without paying their mana costs.