Glad to see you back! Sorry it's under these circumstances.
Yes, what is it that he wants, exactly?
This guy is a monster, clearly. Having been in a similar situation with someone who was intent on suing me and pounding me into the ground -- and suffering PTSD from it long after -- my hope is that you can find a way to detach from his behavior and begin to view him not with power, but with pity. My exNPD will never change. My DS13 is aware of his dad's dysfunction and while he expresses frustration with him, expects nothing different. I don't either. I don't even long for things to be different anymore. He's just an *******, an abuser, and a troublemaker.
My methods of dealing with him include detachment, minimizing contact between us, including neutral drop-offs, asking for nothing that's not in the legal custody agreement, taking zero responsibility for his promises, and doing all communication in text or email. I am never late, and I ask for and apologize for nothing. The times he has called the cops on me, I explained the situation to the cops and they gave both of us a talking to and left.
The thing about those guys that always call the cops? Eventually the cops get sick of making calls about things that aren't crises. It may take awhile, but it happens. My ex has a reputation for being difficult, demanding, and hard to work with. It's great to glide in on my good graces knowing everyone expects him to be bitter and opportunistic.
I deal with it with my son by making sure he knows how much I love him, by spending special time together just the two of us, pointing out where his dad is just wrong (I used to avoid this, but I feel like addressing bad behavior is the right thing to do, and not ignoring it and pretending it's okay or doesn't exist). I am also very active in therapy where I am learning to differentiate myself from my dysfunctional parents, my abusive ex, my alcoholic AH, and all the baggage and low self-esteem that led to a series of bad life choices on my part. The biggest thing? I don't care what he thinks about me. I don't care what he thinks about my life or my parenting. I don't care what he tells other people about me (including gross, deviant sexual things, accusations of drug abuse and child abuse) because I know my truth and I live with integrity. He doesn't. And I know that if we had to stand up in court and lay it all out there, he'd show his ass. He does every time.