In this case, as Zardeck pointed out, this is a stalemate.
Stalemate
The battle is currently a stalemate when neither the Hero(es) nor the Evil Character(s) is being defeated. There are two ways for a battle to be a stalemate: by numbers or by immunity.
At this point, neither side is being defeated. Whoever did not play the last card (your opponent in this case) has initiative. If he cannot play, he must pass to you. At that point, you may play a card or pass. If you pass, the battle is over.
Now, if you had been winning by the numbers, even if his strength was higher than your toughness (let's say he was 10/12 but you were 12/9 instead), he has initiative automatically. If he does not play, you do not get a chance to play anymore enhancements, as initiative does not pass back in a losing condition. By being immune, your hero doesn't care that his strength is higher, and only the EC is losing the battle. If he concedes, his EC is discarded and you win the battle, but no enhancements may be played on your side.
Does that help clear up stalemates?
