Shatterskull Smashing // Shatterskull, the Hammer Pass

In the Commander variant, a double-faced card's color identity is determined by the mana costs and mana symbols in the rules text of both faces combined. If either face has a color indicator or basic land type, those are also considered.

A modal double-faced card can't be transformed or be put onto the battlefield transformed. Ignore any instruction to transform a modal double-faced card or to put one onto the battlefield transformed.

The mana value of a modal double-faced card is based on the characteristics of the face that's being considered. On the stack and battlefield, consider whichever face is up. In all other zones, consider only the front face. This is different than how the mana value of a transforming double-faced card is determined.

If X is 6 or more, you divide twice X damage; you don't assign X damage and then double that damage.

If one of the targets becomes illegal for Shatterskull Smashing, the original division of damage still applies to the still-legal target, but the damage that would have been dealt to the illegal target isn't dealt at all.

If an effect instructs a player to choose a card name, the name of either face may be chosen. If that effect or a linked ability refers to a spell with the chosen name being cast and/or a land with the chosen name being played, it considers only the chosen name, not the other face's name.