Something like this came up a while ago, but since I don't feel like looking up specific card abilities, I'll keep the scenario general:
My opponent rescues with several heroes banded together.
I defend with an evil character with low numbers (so it's my initiative).
I play a card that targets something outside of battle (art, fort, etc.)
Does my opponent get a chance to negate the card I just played before I cease playing cards and lose the battle?