The premise is as follows: A very skilled cheerleader (or gymnast?) has her mind mostly taken over by a stereotypical male action hero (covert or special ops). In times of danger, the cheerleader/gymnast's skills are used in rather frightening ways to subdue (or kill?) attackers.

I'm not sure if I've completely made this up. I know Buffy was a cheerleader and I feel there's some suggestion here to Last Action Hero wherein Jack Slater's daughter pretended at being a damsel in distress before utterly brutalizing her attacker.

If this premise has played exactly as I've described, I don't know who plays the cheerleader/gymnast and who plays the "action hero". I'm pretty sure if it happened, it was live-action and not a cartoon, but it also feels like it was more than a while ago and not a recent idea. I also am not clear whether it was on television. This may have been only one episode.

All that I know for certain is that I can't find any suggestion to it online purely by Googling.

Wait, has Batman ever swapped bodies with a cheerleader?