Demon

Demons are treated as a separate species in the Mortal Kombat universe. Quan Chi, Ashrah, Sareena, Kia, and Jataaka are known demons. They can hide their appearance under a human façade, but otherwise seem to be the same as Oni. Quan Chi was originally a Oni, until he became a demon with his mastery over sorcery and magic.

Other generic demons have appeared in Mortal Kombat: Shaolin Monks as regular minions that players fight later in the game. Shaolin Monks makes no reference to demons such as Ashrah, so it's unclear whether or not these demons are of the same species.