Floor bosses are stronger versions of normal enemies, are named, and are more difficult to defeat. They are identified with a red cape behind their heads that has white horns on it. Floor bosses get standard race bonuses as well as their own bonuses. Note that if a floor boss is polymorphed, it will become a floor boss for whatever race it becomes.
This list is not complete, and it also requires further background information.
Drow: Crowley, regenerates health, named after the Baldur's Gate evil elf-cleric.
Kobold: Pun Pun, max kobold stats, named after the most powerful D&D character ever.
Vampire: Edward, sparkles, named after a character of the Twilight series.
Goblin: Golfimbul, always suffers decapitation, named after the Lord of the Rings character whose fate allegedly gave rise to the game of golf.
Troll: Forchan, level 20 regeneration. He may call you a faggot.
Nymph: The Bitch, always succeeds every steal attempt.
Gorgon: Medusa, attack inflicts slow as well as stun, named after the character of Greek myth that turned people to stone.
Orc: Lurtz, always equipped with a high level bow, named after the Lord of the Rings character who killed Boromir.
Gnoll: Anubis, undead with undead enchanted armor, named after the Egyptian god.
Cactuar: Sabotenquid, confusion attack.
Werewolf: Roulette, polymorphs victim into a random race instead of a werewolf.
Naga: Aapep, fear attack.
Umber Hulk: Khepri, has a random number of lives.
Golem: Frankenstein, made of blood instead of stone, regenerates health.
Banshee: Sadako, can walk through walls.
Mind Flayer: Cthulu, simultaneous fear and confusion attack, named after the tentacled Lovecraftian character.