Can Stand United be legally activated if the only unit at the battlefield is already buffed, and can it target a unit on the bench for the buff?

Ruling: You cannot buff a unit at a different location when playing Stand United from hidden. However, buffed units are legal targets for buff effects, so you can legally activate Stand United targeting your already-buffed unit (though the buff itself will have no effect). The secondary effect that gives +1 to all your units with buffs will still apply.

Sequence:

• Play Stand United from hidden on the battlefield
• Target your already-buffed unit at that battlefield (legal target)
• The buff effect resolves with no change to that unit
• The secondary effect gives +1 to all your units with buffs

Nuances:

• You cannot target a unit on your bench when playing from hidden
• Buffed units are legal targets for additional buff effects even though nothing happens from the buff itself