Somebody we think isn’t going to be able to take down a bad guy in a final confrontation.
BUT THEN HE CAN.
Suddenly, he or she is 50X more adept than we expect after some brilliant and convenient plot device and then we’re blown away by the incredible bad-assery of this man, woman or child.
I know this sounds terribly vague, but the only one I can really think of that does this to any real degree is Neo’s fight with Smith at the end of the first Matrix and the shock as he jumps powers up a level and fights him without even looking at him.
Is there anything else like this? It’s on the tip of my tongue but can’t quiet remember.