Back Off
Card Text & Abilities
[Hidden] (Hide now for [A] to react with later for [0].) [Action] (Play on your turn or in showdowns.) [Stun] a unit. (It doesn't deal combat damage this turn.) If you played this from your hand, draw 1.
Official Rules FAQ & Clarifications
1 Official FAQBlast Cone’s triggered ability that stuns units doesn’t choose them, so Gangplank’s replacement effect can’t apply to that event. Back Off played on a stunned Gangplank does not actually perform the stun game action, because Gangplank is already stunned. It’s legal to play Back Off, but the instruction will be negated. In order for Gangplank’s replacement effect to replace an event of him being stunned, the stun game action must actually be performed. Similarly, if an effect that said “Friendly units can’t be stunned” were active with a friendly empowered Gangplank, Naval is on the board, a stun effect that is played choosing Gangplank wouldn’t generate an event that Gangplank could replace, because no stun game action is performed.
Relevant Rules: 423.1.a.1.