If either target is an illegal target as Thrash tries to resolve, the creature you control won't deal damage.

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.

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.

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.

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.

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 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.

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.