Sorry for waking this up, but I'd like to voice my support for an *Option* to be warned about anything that would kill you. I just played a fully successful run in the Swamp, killed both bosses with LOTS to spare. I was just finishing up remaining monsters just for fun and/or Awards, when I accidentaly attacked a 999 damage-bush. Needless to say, I died, losing more than 30 minutes of progress despite technically already having beat the dungeon, all because I was tired. There's also the fact that *nothing* else on the map could've killed me but one of those bushes, since I was a level 10 Assassin.
I can't speak for everyone, but I know that I play DD both casually and hardcorely - Sometimes I play it just to pass the time and have some fun, often being tired and not at my full awareness, while other times I play with a passion and take on some of the more challenging quests/dungeons.
Just my 10 cents. I just find it frustrating to die like this, and frustration isn't what everyone is looking for, myself included.