I wrote about my experience with him during the Goetia Pathworking experiment in my post on the topic. (Shameless self-plug.)
By far the most interesting experience I had with an entity not in my usual list of contacts. When I first met him, he wound up messing up a whole bunch of things in an effort to “test my mettle” for the rest of the Goetia pathworking experience. I like to think I passed, since the annoying side effects went away.