making bosses better, how could it be done?

There's Pierre's hat thing...

oh god worst boss ever
Why won't he stop cloning himself ahhhhhh

Last I checked, that was random. A group of kaisers or something else could all swing in and easily win.
I'm thinking of something that's like pierre's hat mixed with Akarium's snakes. It chooses what can and cannot damage it class wise, so you'd be forced to partner up with other classes.