Well, I've already spoken of the one where I got killed by 2 shadow bats due to narrow space in another topic (I wasn't quite ready to battle in such conditions), but there was another misfortune that happened fighting a crippled dragon boss in a liutenant tower.
I had only saw the boss blip on the mini map, but couldn't figure which one was (though I had already fought 2 other dragons)... it was one of those vertical boss rooms, and when I land down there, *flame*, right in the middle of dragon breaths, and while I was able to escape most of them, their fire damage ultimately killed me.
In the same spot, I've almost died to my own ghost, unaware that the pink trail they leave was damaging also.