That's a great example. One solution here might be to find an intermediary who works well / gets along with the Toxic boss and involve them in process somehow.

That's a great example. One solution here might be to find an intermediary who works well / gets along with the Toxic boss and involve them in process somehow. You might just go to them for advice and try to understand how they they work with the person and what process has worked well for them. Another one would be to try and meet with your Toxic boss outside the office in a more neutral setting where you can have an open and honest conversation about what's going on. What I've found is people behave and open up differently outside of an office setting. You could also discuss your problem with other folks who work for this person and see if they are coming up against the same problem. If they are, then there are clearer grounds for you all to bring the problem to someone else to try and present it objectively coming 360 review time.