Othainian is a demon encountered during the Underground Pass quest, and is fought during the quest. When killed, he drops the Amulet of othanian, which is needed to obtain Iban's shadow. Protect from Melee should be used during this part of the quest to save life points for coping with Iban's attacks. It is possible to use the small bridges connecting the platforms as a safe spot to attack using Ranged, Magic, or with a halberd. In the quest, the player must also kill the other demons, Doomion and Holthion.
Othainian, along with Holthion and Doomion, are the lowest level demons to drop infernal ashes. However, they are very far from any bank.