Does Facebreaker require both a friendly and enemy unit at the same battlefield to cast, and what happens if one target becomes invalid at resolution?

Ruling: Facebreaker requires you to choose both a friendly unit and an enemy unit at the same battlefield to cast. At resolution, it follows "do as much as you can" principles, but the exact interaction when targets move is still under official review.

Nuances:

• There are two possible interpretations being evaluated: (1) if the enemy unit is moved/removed, the friendly unit still gets stunned, but if the friendly unit is moved/removed, neither gets stunned; or (2) if either unit is moved/removed, neither gets stunned
• This is different from Fox-Fire's targeting restriction
• The "at the same battlefield" requirement may need both units present at resolution to validate the "same" comparator
• If both units somehow move to the same different battlefield, it should work again