I have to admit to my shame that I actually managed to get myself killed by a ratling thief boss monster that got generated when I was still level 1. That was the only time it happened.

I also have to give a huge shoutout to whoever made the goblin boss monster. All these epic try-hard descriptions, and this monster just comes with the description "a small, filthy creature". I met him twice, got a sensible chuckle out of it both times.