Good advice here.
Don't ever trust, let alone confide in, HR.
Be very careful about what you say to other employees. I once made that mistake, and didn't discover until after I was "let go" that she was sleeping with my boss.
The only approach to take, if you wish to stay and fight it out, is to suppress all personal emotion and focus rigidly on how the alleged behaviour negatively affects the company and bring that subject up every time you are required to address the matter. ie:
"This behaviour consumes time and resources that should be better devoted to......"
Be aware that if you take on a narcissistic supervisor that they will lie through their teeth, fabricate evidence, blackmail other employees into testifying against you and of course try and find dirt on you from your private life, past employment, etc. I have seen all that happen.
It should also be noted that in Melbourne we have just seen a female p1ssing contest between Louise Adler, Chairman of MLC and Rosa Storelli, the school principle, which appears to have ended in a draw. If you take on something like that, then good luck to you.