In a nutshell:
- Split cards represent two spells on a single card.
- Casting a split card involves an additional step: choosing which half to cast. This choice is made at the very beginning of the casting process, just before it moves to the stack.
- On the stack, a split card has only the characteristics of whichever half was cast. The others half’s characteristics are ignored.
- Off the stack, a split card has one set of characteristics that is the combination of the characteristics of both halves. For example, Failure // Comply has a mana cost of 1WU, is an Instant Sorcery, is blue and white, etc.
- Split cards only count as one card, spell, etc. For example, if you discard Wear // Tear, that counts as discarding one card, not two. If you cast Wear // Tear fused, you get one prowess trigger, not two.
- Split card specific mechanics include:
- Fuse, which allows you to cast both spells instead of picking a half. The resulting spell will have the combined characteristics of both halves, just like it did off the stack.
- Aftermath, which lets you play the half it’s on from your graveyard (and only from the graveyard). If a spell is cast this way, it’s exiled when it leaves the stack.
Q: What is Breaking // Entering‘s mana cost? What is its converted mana cost?
A: Anywhere except the stack, a split card’s mana cost is the sum of the mana costs of its component halves. Its converted mana cost is calculated based on that total mana cost. On the stack, only the mana cost and converted mana cost of the half that was cast are considered. If a split card is cast fused, the mana cost and converted mana cost of both halves are used. To give a concrete example, Breaking//Entering has a mana cost of 4UBBR and a converted mana cost of 8 in any zone except the stack. On the stack, if it’s being cast fused, its mana cost is still 4UBBR, and its converted mana cost is still 8. If it’s on the stack and the Breaking half was cast, its mana cost is UB and it has a CMC of 2; if the Entering half was cast, its mana cost is 4BR and it has a CMC of 6.
Q: Can I get a Failure // Comply with Burning Wish?
A: Yes. Anywhere off the stack, including outside the game, Failure // Comply counts as both an instant and a sorcery. Because it’s a sorcery, you can get it with Burning Wish. This is exactly like how you can get artifact creatures with Golden Wish.
Note: On the stack, only the characteristics of the half that were cast exist. The other half’s characteristics are ignored. So you could Dispel a Failure or Envelop a Comply, but you couldn’t do that the other way around.
Q: Can I name Wear // Tear with Meddling Mage?
A: Sort of. You can certainly pick split card names for anything that asks you to choose a card name, assuming they fit any other requirements for picking the name. You can only pick one of a split card’s names though. So you could pick “Wear” or “Tear” but not both. Whichever half you named can’t be cast. Whichever name you pick, it will stop Wear // Tear from being cast fused, since that spell has both the name “Wear” and “Tear.”
Q: Can I get two Fire // Ices with Gifts Ungiven?
A: No. Each Fire // Ice you get will have the names “Fire” and “Ice.” They have at least one name in common, so they are considered to have the same name.
Q: Amy reveals Wear // Tear with Counterbalance. What converted mana cost spells can she counter?
A: Off the stack, Wear // Tear has a mana cost of 1RW and a CMC of 3. Amy will counter any spell with CMC of 3, but not one with CMC 1 or 2.
Q: Can you target Commit // Memory with Torrential Gearhulk? Can you play either half?
A: Off the stack, Commit // Memory is an instant (and a sorcery), so it’s legal to target it with Torrential Gearhulk. You can pick either half because the process of casting Commit // Memory involves picking a half to cast, and Torrential Gearhulk’s ability doesn’t put any constraints on that choice. Memory’s aftermath ability says the spell can only be cast from a graveyard, but that’s what you’re doing, so there’s no problem there either.