Derro

A small dwarf-like species that inhabit the Undervale. Dwarves deny any shared lineage, noting that the only similarity is in their short and stocky stature. Derro are considered to be quite mad by most other species, but their natural cruelty and lust for torturing others without any discernible reason makes them feared by most and sought after by some looking to use them to torment their prisoners or enemies.