my final battles will not use mechanics the players aren’t familiar with

This seems kinda boring.

I pretty much expect a big bad to pull some off the wall crap I’m not expecting, otherwise what makes them big & bad?

The morale shattering of getting a revival countered would make the party come up with something new, instead of trying their same formula over & over. Remember the magic mcguffin they’ve been saving for a ‘situation’? This is exactly the time to break out the one-shot items!