Ultimate Skill Fallen King Lucifer was the original Ultimate Skill wielded by Dino before gaining Slothful King Belphegor. Most of its exact abilities are unknown but Dino himself described it as a weaker mixture of Wrathful King Satanael and Prideful King Lucifer. Despite having the properties of both, Dino claimed he would be at a disadvantage in a battle against either due to the inferiority of effect.
Fallen King Luciel used to be Sky King Luciel until Dino acted on his own accord to have revenge on the country that killed his master and creator, Veldanava. This caused his race to transform from a Seraphim to a Fallen, and his Ultimate Skill transformed accordingly as well.
To prevent confusion with Prideful King Lucifer [Rushifaa], Fallen King Luciel was translated as Luciel instead of Lucifer [Rushiferu]. However, since some sources say Lucifer's original name was Luciel before he fell, it works out.