Boss Monsters are a species in Undertale. They are creatures whose souls can temporarily exist outside of their body after death, and they only age when their offspring does, unique traits compared to other monsters in the game.

All currently known Boss Monsters are members of the same royal family, the Dreemurr family: Asgore, Toriel, and Asriel. They display a mix of caprine and lion-like features such as fangs, paws, droopy ears, and horns when matured. Similar to real life lions, they appear to display sexual dimorphism, with males often having manes. They also appear to have unique magical powers of sorts, often dealing with or themed around flames or fire, a possible nod to and deconstruction of the tropes surrounding satanic and demonic caprines.

While all Boss Monsters are encountered as bosses ingame, not all bosses are Boss Monsters. Boss Monster refers to the unique, caprine-like species seen in the universe of Undertale, not all monsters who happen to be bosses. While deliberately very similar in appearance to Asriel, it is unknown if Deltarune's Ralsei is also a Boss Monster, and therefore they should not be tagged as such.

In the unofficial fan game Undertale Yellow, two other Boss Monsters are observed: Chujin Ketsukane and his daughter Kanako. Unlike the Dreemurr family, the Ketsukane family have fox-like features, including tails and long snouts, and seem to be based on mythological kitsune. Despite being a part of the same family, Ceroba is not a Boss Monster.

See also

• caprine
• video_games
• deltarune
• undertale
• asgore
• asriel_dreemurr
• toriel