I think. I hope it works.
There is nothing like the muse announcing that obviously what happens here is that the character does Something Clever with the magic already introduced -- in this case, magical stones with great but not immediately or obviously useful powers -- using it in an ingenious manner so that the more powerful villain falls before it in a convincing manner. And then goes off to play with building blocks, having obviously done her fair share on how to resolve the plot. (Did I mention this is the proposed climax? It is.)
the other thing is that it's supposed to be a dramatic climax, not a comic one. And to qualify as dramatic, it needs to have the real possibility of failure. Which means it can't be too clever. If it's obvious that the heroine will go trample the villains who have threatened the entire kingdom, it kinda knocks the stuff out of the villains, too. How dangerous can necromancy be if they can be defeated without danger?
But I've worked out a plan to trick the necromancers into using something they shouldn't, and so trap them. Let's see if it's as convincing in prose as in outline.