Can Mistfall be used on an opponent's turn if Stand United is used as a reaction on the opponent's turn?

Ruling: Yes, Mistfall can be used on an opponent's turn. Mistfall is a triggered ability that activates any time a friendly unit is buffed, regardless of whose turn it is.

Nuances:

• Mistfall does not need to say "reaction" to be used on an opponent's turn; it triggers automatically whenever its condition (buffing a friendly unit) is met
• Stand United can buff during an opponent's turn as a reaction, which would trigger Mistfall