The Blue Fiend is an enemy encountered in Lunar: Eternal Blue and its remakes. It is found deep within the Blue Dragon Cave, next to the entrance of the Blue Dragon Lair, stationed there to keep the party from entering the lair. Thus, forcing the party to do battle with it.
It is the second of four Fiends encountered in your journey to access the Goddess Tower.
In Eternal Blue, the Blue Fiend was presented as serpent-like in appearance, while in Eternal Blue Complete, it was presented as fish-like in appearance.