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. For example, if an effect prevents you from casting red spells, you can cast Road, but not Ruin.

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 instant and sorcery cards in your graveyard, Road /// Ruin counts once, not twice.

Each split card has two names. If an effect instructs you to choose a card name, you may choose one, but not both.

While not on the stack, the characteristics of a split card are the combination of its two halves. For example, Road /// Ruin is a green and red card, it is both an instant card and a sorcery card, and its mana value is 6.

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.

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.

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.

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.

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.