You may put two +1/+1 counters on a creature you control. Then all creatures get -4/-4 until end of turn.
(08/12/2022)
To cast a split card, choose one of its halves to cast. There's no way to cast both halves of this split card.
(05/10/2018)
Finality doesn't target the creature to receive +1/+1 counters. You can cast it even if you control no creatures.
(08/12/2022)
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.
(08/12/2022)
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.
(08/12/2022)
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.
(05/10/2018)
Finality affects only creatures on the battlefield at the time it resolves. Creatures that enter the battlefield later in the turn won't get -4/-4.
(08/12/2022)
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.
(08/12/2022)
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.
(08/12/2022)
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.
