The Mustafar mission involved an unknown traveler working alongside the spirit of Jedi Master Obi-Wan Kenobi to fix a disturbance in the Force on Mustafar. Kenobi tasked the traveler with finding a shard and neutralizing its influence to restore balance and eliminate the dark side's hold on the planet. After finding the shard, the traveler attempted to return it to its chamber, but first had to face the Dark Jedi Vartonis and his Brotherhood Mortalis mercenaries. The traveler defeated them and successfully restored balance for Kenobi.
Long ago on Mustafar, events triggered a major disturbance in the Force, which amplified the dark side's power on the planet. The Jedi Order once had a chapter there and discovered a large crystal with an unknown origin. The Jedi learned that it resonated with their individual Force abilities. However, when news of an impending Sith invasion arrived, they experimented with the crystal, hoping it would help defend the chapter. The Jedi believed that channeling their powers through the crystal would enhance their abilities and significantly weaken the Sith. Although it initially worked, the crystal gradually began to crack under the strain of the power being forced through it.
The crystal's explosion sent the planet out of orbit, killing all Jedi and Sith except the elder Jedi Master Erg Krow. As the crystal detonated, he managed to protect himself from some of the resulting devastation, and despite being injured, he discovered that a large piece of the crystal remained relatively intact. Krow went into hiding with the shard, using the last of his strength to create a protective Force shield around it to prevent other Force-sensitive's from detecting its presence. Krow died soon after, and the shield he created gradually weakened over millennia.
As time passed, rumors of ancient treasure circulated, attracting adventurers to Mustafar. However, whispers about the crystal also drew darksiders to Mustafar, including the Dark Jedi Vartonis, who hired the Brotherhood Mortalis to help him secure the shard and amplify his power in the dark side of the Force.
Obi-Wan Kenobi, as a spirit - months after his death on the first Death Star - appeared on Mustafar to find a way to eliminate the dark presence and restore balance. Unable to act directly, he sought the help of an unidentified spacer. He warned the spacer that the dark side was growing stronger and that failure to restore balance would further empower it.
Kenobi revealed to the spacer that the remaining shard contained the trapped soul of a Jedi. He was certain that this shard could be used to enter Krow's chamber. Kenobi requested that the spacer recover the shard so it could be destroyed, preventing it from falling into the hands of dark siders.
The spacer located the shard in the possession of an unhinged Mustafarian hermit, whose erratic behavior made it difficult for even Kenobi to find him through the Force. Kenobi believed that the Jedi soul within the shard was in great pain and that it may have gradually driven the hermit mad. The hermit became hostile, and was killed during the confrontation. While Kenobi expressed regret over the hermit's death, the spacer insisted that the confrontation was unavoidable, which Kenobi conceded.
Kenobi and the spacer located the Lair of the Crystal, and Kenobi sent the spacer ahead to find it while he delayed the dark siders who were hunting for the crystal. The chamber was north of the central volcano in the Burning Plains, in its northeast corner. When the spacer arrived, Kenobi's spirit returned. Inside the inner chamber, Vartonis and the Brotherhood Mortalis members arrived, hoping to claim the crystal shard. The spacer confronted and defeated them.