If a card in a graveyard has in its mana cost, X is considered to be 0.

To double a player's life total, that player gains as much life as needed so that their life total is twice the number it was before. If their life total was negative, that player loses as much life as needed so that their life total is twice as far below 0 as it was before. Other effects interact with this life gain or loss accordingly.

If an effect allows you to cast a spell with certain characteristics, consider only the characteristics of the half you're casting. For example, if an effect allows you to cast a sorcery spell with mana value 2 or less from among cards in your graveyard, you could cast Assault this way, but not Battery.

A split card's characteristics are a combination of its two halves while it is not on the stack. For example, Assault // Battery has a mana value of 5 while it is in your library. If an effect allows you to search your library for a card with mana value 4 or less, you can't find Assault // Battery.

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

Each split card is a single card. For example, if you discard a split card, you've discarded one card, not two. If an effect counts the number of sorcery cards in your graveyard, Assault // Battery counts once, not twice.

Split cards have two card faces on a single card. The characteristics of the half you didn't cast are ignored while the spell is on the stack.

To cast a split card, choose one of its halves to cast. There's no way to cast both halves of this split card.

If you copy a spell that's half of a split card, the copy copies that same half. For example, if you copy Assault, the copy is also Assault, not Battery.