During his fealty to Darth Sidious, the mutant genetic terrorist Zeta Magnus dispatched a clone decoy of himself to invade the planet Marat V. While this clone was cut down by Jedi Padawan Halagad Ventor, the real Zeta Magnus was alive and well in the Unknown Regions.
An Arkanian geneticist
During his thirty year tour around the galaxy, Magnus gathered not only knowledge, but also many slaves and followers. He used these adherents to carve out his own kingdom in the Unknown Regions called the "Dark Worlds". It was during this time that Zeta Magnus discovered that his creators had programmed an expiration timer into his DNA. During his subsequent search for immortality, he was approached by Darth Sidious. The Dark Lord of the Sith offered the dying mutant the secrets to eternal life in exchange for his fealty to him. Magnus accepted and helped bioengineer many weapons for Sidious' Separatist minions. In order to throw the Jedi off Sidious's trail (and also to subtly mock his new master), Zeta Magnus adopted many aliases of Sith origin and adorned himself in the armor of the Sith-aligned Magi Sentinels. Magnus's deception successfully led many Jedi such as Jedi Master Mace Windu and Jedi Padawan Halagad Ventor to suspect Zeta Magnus as the second Sith.
A S'ktri
During the early phases of the Clone Wars, Zeta Magnus created a clone of himself and flash pumped his memories into its mind. The clone believed he was the real Zeta Magnus and did not realize he was a clone. The Magnus clone ventured to the Outer Rim planet Marat V and made made contact with the native S'kytri of the Outland Clan. Outlanders were S'kytri who embraced a life of walking rather than flying. Making up a third of the planet's population, their numbers also consisted of S'kytri who were considered aberrant because of reversed skin pigmentation or disfigurements. In the past, the Outland Clan served as indentured serfs for the Lowland Clan. Over time, the Outland Clan was allowed to live as they please and Marat V saw relative peace as the Outland, Lowland, and Highland Clans bartered with each other.
A mutated Outlander.
Magnus promised the Outland Clan that he would increase their farming production with advanced scientific techniques and that he could cure their stigmatizing pigmentations. Once all the Outlanders flocked to his banner, he unleashed a virus into the air that ravaged their minds and turned them into savage, zombie-like followers. Since the Outlanders were responsible for most of the agriculture on Marat V, Magnus's plague caused two-thirds of the planet's population to starve. Magnus then cut off the S'kytri's communication to outside worlds and proclaimed himself the "Magister of Skye". He constructed an opulent fortress atop the sacred Canaitith Mountain and populated the Entyrmion caverns underneath it with Oskan blood eaters that he grew as watch beasts. While Magnus dined on the flesh of his S'kytri followers in his citadel, his Outlander mutants carried out multiple suicide raids against Lowland and Highland Clan mountain fortresses.
The Golandras.
When the Republic learned of Zeta Magnus's subjugation of Marat V, they dispatched the MedStar-class frigate Golandras to deliver food and aid to the plague-stricken world. Accompanying the mercy mission was Jedi Knight Obi-Wan Kenobi, Jedi Padawans Halagad Ventor and Anakin Skywalker, and a squad of clone commandos. When the Golandras was destroyed by a cloaked minefield in Marat V's orbit, the Jedi/clone strike force evacuated in escape pods. Upon reaching the surface, they moved to carry out their true mission: to arrest Zeta Magnus and free the S'kytri. As the Jedi met with the Supreme Council of the Highland Clans, the Magnus clone released a HoloNet News transmission accusing the Jedi of interfering in his sovereignty over Marat V and ordered them to be recalled lest he unleash a plague upon the worlds of the Republic.
Jedi Padawan Halagad Ventor killed the clone of Zeta Magnus.
Once the Jedi reached the summit of Canaitith through the Entyrmion caverns, the S'kytri clans went into battle against Magnus's Outlanders.
With Zeta Magnus seemingly dead, another lead in the Jedi's search for the second Sith had gone cold. The outcome of the Battle of Skye was reported by Blue-Tark to the original Zeta Magnus who was at his Rennek Palace in the Dark Worlds. After hearing the report, Zeta Magnus stayed true to his promise and unleashed multiple plagues unto an untold number of Republic worlds.