All split cards have two card faces on a single card, and you put a split card onto the stack with only the half you're casting. The characteristics of the half you didn't cast are ignored while the spell is on the stack.
(2022-04-29)
Each split card has two names. If an effect instructs you to choose a card name, you may choose one, but not both.
(2022-04-29)
Once you've started to cast a spell with aftermath from your graveyard, the card is immediately moved to the stack. Opponents can't try to stop the ability by exiling the card with another effect.
(2022-04-29)
Each split card is a single card. For example, if you discard one, you've discarded one card, not two. If an effect counts the number of sorcery cards in your graveyard, Indulge /// Excess counts once, not twice.
(2022-04-29)
A spell with aftermath cast from a graveyard will always be exiled afterward, whether it resolves, it's countered, or it leaves the stack in some other way.
(2022-04-29)
Excess counts the number of creatures you controlled that dealt combat damage to a player even if you no longer control one or more of those creatures as it resolves.
(2022-04-29)
If another effect allows you to cast a split card with aftermath from any zone other than a graveyard, you can't cast the half with aftermath.
(2022-04-29)
If another effect allows you to cast a split card with aftermath from a graveyard, you may cast either half. If you cast the half that has aftermath, you'll exile the card if it would leave the stack.
(2022-04-29)
While not on the stack, the characteristics of a split card are the combination of its two halves. For example, Indulge /// Excess has a mana value of 5.
(2022-04-29)
If you cast the first half of a split card with aftermath during your turn, you'll have priority immediately after it resolves. You can cast the half with aftermath from your graveyard before any player can take any other action if it's legal for you to do so.
(2022-04-29)
