Lucisfear

Lucisfear, Formido Ex Lumine (translated and adapted to Lucisfear Terror from the Light), is very technically a nega-saver servant formed by a composition of parallel and deviated versions of the Godslayer due to a summoning in the lanes. It is assumed from his introduction monologue his main objective is to spread death.

Appearance
Tall as hell, variant length black hair, red eyes, usually wears a red trench coat with a suit underneath.

His and Kuon's faces are nearly identical, with only a slight difference in hair coloring.

Rapture ~ The denial of existence
Lucisfear seems to have an unique version of the Rapture, manifesting black instead of red. It can be interpreted as the Rapture's contrarian, so if the Rapture is the creation of possibilities, Lucisfear's Rapture is the elimination of possibilities.

It is unknown how this differentiation is even possible and how it relates to the requirements by which Rapture may be used.

Future elimination
Possibly THE best defensive ability; any and all future events where Lucisfear is damaged are automatically destroyed (this effectively means he could put your hands over his neck and you still wouldn't be able to do anything to him).

The only way to get through this protection is an equal force. There are also some specific artifacts that can go through, Chaos's Last Word, Kuon (incomplete Rapture), and Omega's Lumina; it is unknown why this is possible, but we shall call these artifacts  fatebreakers .

Godslayer's mercy
Lucisfear can at any time choose to execute any one person that has fallen into despair or desires death, be it due to grieft, sadness, anger, etc. During this time, Lucisfear can warp to the chosen person or send a wraith to the person's location; during this ability Lucisfear is intangible and only interruptible by rapture.

The Night of Fallen Angels
Upon awakening, Lucisfear activated this ability, progressively sieging worlds through an army of wraiths commanded by the Hell-Sent Bullet. During this ability, the sky and the sun turn pitch black, the latter acquiring a white stellar corona.

Salvation
Lucisfear can activate a worldwide Godslayer's Mercy during the Night of Fallen Angels, each execution appearing as a pillar of blue light ending in a cross.

The Idea of Evil
Lucisfear can corrupt any person, object, location, and others, effectively taking control of them and/or changing them drastically. People need to receive direct eye contact, physical, or ethereal contact of some form, objects can be corrupted and manipulated from any location disregarding time (Lucisfear was able to manipulate Astora's Excalibur from the future, and his presence in the same room was enough to instantly shatter it).

Dreams of the Black Throne
Lucisfear can utilize this corruption to instigate a forced EGO meltdown and subsequently create a berserk distortion as was the case with Ciel.

Godslayer's Inferno
Lucisfear and The Hell-Sent Bullet's ranged attacks must be destroyed (HSB's bullets can also be blocked, but not by terrain unless it's actively used as a shield, and not just stood behind), and their attacks are automatically redirected towards their target. In addition, Lucisfear's attacks cannot be destroyed or deflected unless one is using Rapture, an artifact of Genesis, or a fatebreaker.

Memento Mori
Lucisfear and all of his deviations (except for wraiths used during The Night of Fallen Angels) have their attacks coated in an unknown poison that deactivates healing and disintegrates the opponent with a single bullet. The only person that has been shown to be able to remove this effect is Kuon by severing it through Rapture, it is assumed The Composer and Excellion can do the same.

Trivia

 * His name is a play on Lucifer (Satan, fallen angel), one of the latin words for "light" and fear, a localized and stylized version of his title "Formido Ex Lumine".
 * "Formido Ex Lumine" is a title inspired by the name for the trope "Deus Ex Machina" (which is also a reference to the fact hat he was summoned from a machine)
 * His eye color should technically be golden, but design constraints.
 * He's inspired by force of nature villains like the Joker (Batman).