Sylux is a powerful Bounty Hunter who appeared in Metroid Prime Hunters. Very little is known about Sylux, other than that it harbors a strong hatred for the Galactic Federation, and Samus Aran by association.
Very little is known about this character or why Sylux hates the Galactic Federation and Samus Aran. Sylux harbors a strong hatred for fellow Bounty Hunter, Samus Aran, for working with the Federation.
Looking at the overall humanoid shape, and the humanoid hand holding the Shock Coil (Sylux's weapon of choice), it is possible, and sometimes assumed, that Sylux could be human. This theory is also backed partially by the use of stolen Federation gear and armor, which seem to be human in shape, however, Sylux's species in the cinematic intro to Metroid Prime: Hunters is labeled as "unknown." Sylux is seen fighting Federation soldiers in a location called 'Cylosis'.
Sylux's ship is the Delano 7, a blue X-shaped ship with aerofoils similar to the Lockjaw form. Along with Samus' gunship, Rundas' Phrygisian-class gunship, and Ghor's Battlesuit/gunship combination, the Delano 7 is one of the few hunter ships to appear in the games themselves, although Weavel's spaceship makes a small appearance in a docking bay during the cutscene for landing on the Oubliette.
In the Special Ending of Metroid Prime 3: Corruption, Samus departs for space in her Gunship. She is unknowingly followed by a mysterious spacecraft. For years after the game's release, it was speculated that the pilot of the ship was Sylux. At E3 2015, the producer of the Metroid Prime series, Kensuke Tanabe, confirmed that the pilot was in fact Sylux. He referred to Sylux using male pronouns and expressed his desire to create a game revolving around Samus and Sylux. This potential Metroid Prime 4 would be released after Metroid Prime: Federation Force, which is meant to flesh out the role of the Galactic Federation in the series.
The ending of Federation Force shows an individual with armor resembling Sylux's breaking into a Federation facility and hatching a Metroid Egg in a stasis tube. This may hint towards a future Metroid Prime game involving Samus and Sylux, that also leads into Metroid II: Return of Samus.
Like all other Hunters in the game, Sylux is capable of defeating Samus and taking one of her Octoliths. In order to complete the game, Samus needs all of the Octoliths, and thus must fight her thief again in order to gain it back.
Sylux's weapon is known as the Shock Coil. The Shock Coil was a prototype weapon under development by the Galactic Federation. It is an illegal combat technology: It fires a continuous beam of concentrated neutrinos at its target. It was eventually stolen by Sylux, along with a prototype suit and ship, the Delano 7. The Delano 7 is encountered twice in the game, and it is the only Hunter ship other than Samus' seen (in detail) in the game. Interestingly, despite hating the Galactic Federation, Sylux currently only uses equipment that was designed and made by them.
Sylux has an alternate form known as the Lockjaw. In this form, Sylux becomes a ball of green energy the size of Samus's Morph Ball form, surrounded by two entwined, metal bars that look like a deformed version of the Delano 7 with energy threads connecting them together. Sylux can deal a large amount of damage in this form and is quite agile. While in this form, Sylux can drop two Electric Bombs and connect them, unless there are obstructions or they are set too far apart.
Super Smash Bros. Brawl
Sylux has also appeared as a trophy in Super Smash Bros. Brawl. It is the only one of the hunters' trophies that is referred to as an "it" instead of a "he" or "her" pronouns.
"A skilled marksman and bounty hunter experienced in espionage skills such as scouting and tracking. While much of its background remains a mystery, it is clear that it hates Samus and the Federation. Sylux uses the Shock Coil, an experimental Federation-made weapon that continually drains energy from enemies and refills its own."
Nintendo DS Metroid Prime Hunters
- Sylux Metroid Prime Hunters - [Specials: Indirect] Attack +12 (All)
Metroid Prime Hunters manual
"Sylux is a resourceful tracker, and a deadly sharpshooter who harbors an intense hatred for the Galactic Federation and for Samus Aran for assisting the Galactic Federation in the past"
Nintendo Power March 2006
"Sylux's background is unknown, but the hunter's motives are clear - to crush the Galactic Federation. Using technology suspiciously similar to a stolen Federation prototype, Sylux can deploy blades that travel along beams of energy while the hunter is in ball form." 
This hunter's power suit appears to be based on a federation prototype and possesses extraordinary offensive and defensive capabilities. SYLUX's weapon is the SHOCK COIL, a banned technology that fires charged blasts of high-density NEUTRINOS.
"Little is known about the mysterious bounty hunter known as Sylux, other than the fact that Sylux harbors an intense hatred for the galactic federation and the bounty hunter who has helped the Federation time and time again... Samus Aran."
- The Metroid Prime Hunters Official Nintendo Player's Guide incorrectly states that Sylux turns invisible when equipped with the Imperialist. This exact same sentence is used on Trace's page. Ingame, Trace is the only one who can turn visible.
- Sylux's Lockjaw form is designed very similar to Samus's own Morph Ball. It has a storage of three bombs and has the same glowing green orb. The alternative form may suggest that the Galactic Federation has begun to construct prototypes of Samus's gear, which is further progressed with the downloadable data in Metroid Fusion.
- Metroid Prime Hunters
- Metroid Prime 3: Corruption (Delano 7 appearance.)
- Super Smash Bros. Brawl (Appears as a trophy and sticker)
- Metroid Prime Hunters Official Nintendo Player's Guide
- Metroid Prime: Federation Force (possible appearance)
This is the music heard when battling Sylux: 
| Samus Aran|
'Big Time' Brannigan • Armstrong Houston • Zegan Doh
Sylux • Weavel • Kanden • Spire • Noxus • Trace
Rundas • Ghor • Gandrayda
Dark Panda • HWCASE • Georgia McHenry