It is basically impossible, yes (I believe this is touched on in the recent Roguelike Radio interview. Suffice it to say: 16 colors is all you've got, for everything).
You meet Nezic, the lich.
This powerful undead creature refused to surrender to death even when life had fled the body, and now exists through dark magics that maintain its skeletal form. Its touch is dangerous as any life can feed the lich's need to force life upon itself in spite of the passage of time.
(the usual lich description)
Met it on D34, killed it with undead slayers to avoid risk, no special powers noted.
Hobbynobs, the hobgoblin
The ugly hobgoblin looks crafty and sly. He seems to be the kind of hobgoblin who delights in stealing important artifacts and killing innocent puppies.
Can cast spell: invisibility.
Tarmo the Foolish, the minotaur
At first glance you mistake this creature for one of the undead. The skin is torn and rotten and nearly all the creature's fur has fallen out. As it shuffles on torn and rotting muscles, you see that it still yet breathes. You know not what disease or curse has afflicted this being, but the pain has driven it mad. Now it seeks only to make others suffer as it does.
Mar "The Fiery Kraken", the fire vortex.
Before you stands a humanoid manifestation of elemental energy, it is unmistakably Mar, "The Fiery Kraken". Mar is an inferno of hate, burning fiercely in a multitude of erratic colour. Gangly limbs extend as if pulled from their sockets and trash at you with ill-meditated direction. An unrelenting screech shokes the air, and Mar approaches...
You meet Antharaxa, the female tarantula.
This spider has eight legs and many eyes but the similarities with its lesser cousins end here. For one thing it is larger than an ox. Its many eyes shine with an unusual intelligence and its fangs drip a vicious venom. Oh, and it rushes towards you with unnatural speed right now...
The beast before you is a solid wall of thick muscles from head to toe. His skin is drawn tight across his body exposing the muscles and thick rope like veins. Many scars are visible along the arms of this ogre which, combined with the blood and the aroma of rotting flesh leave you with the impression he will not be easily overcome.
Jo'ohr, the female kobold shaman.
Sorry, didn't manage to copy the flavor text. Has a confusing attack as well as the usual shock bolts. She would be nasty for a low-level PC, but met her in the Big Room at level 24.
Like other people, I've happened upon multiple instances when the message was generated but no boss monster could be seen on the level, even with a blessed wand of monster detection. I suppose it's possible the boss got insta-killed by other monsters, but several times?
I ran into Soladnit again (hell hound that can walk through walls). The game doesn't give his introduction when he enters LOS, only when he enters a non-wall square in LOS. Has anyone else noticed stuff like this happening for these types of boss monsters?
Like other people, I've happened upon multiple instances when the message was generated but no boss monster could be seen on the level, even with a blessed wand of monster detection. I suppose it's possible the boss got insta-killed by other monsters, but several times?
I agree, it happens often enough that it's probably a bug.
You steal a scroll labelled HITME. The orc hits you.