The Duel on Mustafar was the event in the Great Jedi Purge in which Darth Vader was injured by Obi-Wan Kenobi, and would later be transformed into his cybernetic form. It would prove a decisive moment in Galactic history, as had Obi-Wan lost, he would have not gone into hiding and Luke Skywalker would have not become a Jedi.

The two battled each other on the landing platform and made their way through the hallways of Klegger Corp Mining Facility. In the conference room, Vader and Kenobi each tried to kick each other mutiple times, in which Anakin forced Kenobi's lightsaber handle into his throat, temporarily paralyzing him, and attempted to decapitate his former master. Kenobi held off as best he could. Kenobi managed to fling himself out of his former Padawan's grasp. Then, he knocked Anakin down and called his lightsaber to his hand, thinking he could put Anakin at blade-point, forcing a surrender. He failed and the two proceeded into the control room. The two forced each other into opposite ends of the room with a combined Force push. Attempting to kill Kenobi, Vader jumped at the Jedi and missed, accidentally destroying the controls for the facility's shields, allowing heat and flying lava to weaken the collection arm systems outside the complex.

As the two dueled on, Anakin forced Kenobi back in a furious attack. While this was going on the lava collection arms outside, the lack of shielding proved too much for the superstructure, bringing it down. It smashed into the river of lava, and both contestants barely held on for dear life. The lava river below dragged the collection arm down a lava-fall and nearly killed Vader. However, both he and Kenobi managed to leap off the arm, landing on a droid lava collector and a repulsorlift platform, respectively.

It was then that Kenobi accepted that Anakin was consumed by Vader, and realized the Sith before him would have to die. As the two dueled their way to the shore, Obi-Wan leapt, gaining the high ground over Vader. In his rage and overconfidence, Vader made a blunder and risked his life jumping after Obi-Wan, losing half of his left arm and his two legs severed around the knees in a blink of an eye. He tumbled down to the shoreline, maimed and immobilized.

Kenobi took Anakin's blue lightsaber whilst sorrowfully expressing his regrets. Vader's clothing ignited from the nearby lava at Mustafar's hot shore, burning him horribly. Kenobi refused to kill the Sith Lord, believing that his ultimate fate would be decided by the Force, and left Vader for dead as the flames slowly calmed down from the graphic immolation he witnessed.

Palpatine, sensing that his new apprentice was in grave danger, left Coruscant after a duel with Jedi Grand Master Yoda, and, accompanied by a squad of shock troopers, journeyed to Mustafar in a Theta shuttle. They landed in the Klegger Corp Mining Facility and recovered the dying Sith apprentice. Darth Vader's maimed, crippled and burned body was taken to Coruscant and the Emperor Palpatine Surgical Reconstruction Center for treatment in order to save his life. There, he was transformed into a cyborg. Darth Vader would wear a respirator and full body suit for the rest of his life.

Padmé Amidala's injuries on Mustafar, as well as the horror of seeing her husband consumed by the dark side, led to her death in childbirth-giving birth to Luke and Leia-on Polis Massa. Kenobi went into exile after helping to deliver Anakin's children on Polis Massa. He took Anakin's infant son Luke to Tatooine to be raised by Anakin's stepbrother and his wife, while his twin sister, Leia went to Alderaan to be raised by Bail Organa and Queen Breha. Kenobi hid on Tatooine, waiting for the day when Luke would be trained as a Jedi.