So ultimately it didn't make a difference in the outcome of the game... but I have a question on Unstoppable.
(Here is the wording on the card for reference: "Unstoppable: Play during your opponent's Attack Step when a friendly unit would be eliminated by an adjacent enemy unit. Before that unit is eliminated, it may counter.")
My Citadel Guards attacked my opponents Blood Harvesters - my attack got him down to a single Blood Harvester and forced a retreat which would push him off the map... essentially killing the unit off completely.
He played Unstoppable to attack before he was destroyed - he argued essentially that the retreat I rolled destroys the unit so he should get to use the card to get in the counter attack. I disagreed as I felt that the retreat would essentially have removed his adjacency - even though it's the inability to perform the retreat that kills the unit off... (Regardless - I chose not to argue as I was very much in the lead at this point and didn't want to make any bad feelings when the victory was pretty much a foregone conclusion at this point etc.)
Thoughts? Did we play it right with him getting in an attack? Or should that card not have been playable?