Palpatine's changed appearance in Obi-Wan Kenobilikely reflects 10 years of aging and further deformity from continued use of the dark side of the Force.
Windu eventually gets the better of Palpatine before deflecting his Force Lightning back against him, which appears to twist and melt Palpatine's face as his body begins to smoke, turning him into the grotesque embodiment of the Sith that acts as the final antagonist for both Star Wars: Episode VI - Return of the Jedi ...
Years after his death, during her duel with Jacen Solo, Lumiya alluded to Palpatine, saying he was a "psychopath consumed by power.". Palpatine's manipulative behaviour cannot be exaggerated as he manipulated the entire galaxy into doing his bidding.
In the novelization of The Rise of Skywalker, Kylo Ren deduced that Palpatine's dark side spirit and power were too strong for the clone body to handle, causing major deterioration, which is known to happen to many dark side users – the stronger they get, the more damage to their physical bodies.
And his body was too messed up and unnatural to reproduce. So he went with the cloning, gene-splicing route. However Palpatine's cloned bodies could not bear his malevolent spirit, without them decaying. He eventually would have a “son”.
The Actual REASON Palpatine’s Face Changed (NOT Sith Alchemy) - Star Wars Explained
Who is Palpatine's clone son?
The Emperor's son
Emperor Palpatine's "son" was a strandcast cloned from his genetic template. Dathan was an artificially constructed strandcast from the genetic template of Sidious. and the lone specimen that lived through the cloning process.
Palpatine carried the lightsaber for a great deal of his life afterward, though he only rarely wielded it in combat, as his position as Emperor made battles with other Force-users few and far between, and he preferred to rely on his raw ability with the Force in any case.
As the Death Star had been destroyed, and the Battle of Yavin had finally taken place, the years then moved into ABY (After the Battle of Yavin). It's said that Star Wars: Return of the Jedi takes place during 4 ABY, meaning Palpatine was 88 when he met his original end.
While George Lucas has never officially commented on it, it's agreed upon that when someone's eyes turn yellow, it means they are fully immersed in the dark side of the Force. They've lost control of emotions such as hatred, letting the dark side take over momentarily.
Palpatine's face was left disfigured after fighting Mace Windu, but despite Star Wars' medical technology, he never tried to heal his scars. In Star Wars: Revenge of the Sith, it was revealed that Emperor Palpatine's face wasn't just the product of old age but also scarring from fighting the Jedi.
But the Obi-Wan Kenobi finale includes a beat where Obi-Wan, having realized his friend is gone, calls him "Darth" instead of Anakin, suggesting this was always his way of acknowledging that Anakin has become something else entirely.
He understood he lost the ethereal battle before their physical fight even began. Thus, Palpatine never viewed Yoda as a major concern, even though the Jedi Master fought him to a de facto draw during the events of Revenge of the Sith.
If Rey struck him down, Palpatine's spirit would pass into her, allowing the Sith to be reborn. Rey resisted him with the help of Ben, who'd returned to the light. But their defiance gave Sidious a new opportunity – he would drain the energy of their Force dyad to restore his own body, then rule alone.
Rumor had it that his mother was Palpatine's Umbaran aide Sly Moore, who had impregnated herself using DNA from an undisclosed source. Regardless of the veracity of that report, Triclops was regarded as the true son of Palpatine, both by himself and the few high-ranking officials who were aware of his existence.
Though Yoda and Qui-Gon respected each other, they were often at odds due to their differing beliefs; Yoda looked to the future while Qui-Gon lived in the moment.
She replies, "Myself," to which Luke says, "Because you're a Palpatine. Leia knew it, too" This realization takes Rey by surprise, as there had been few hints about her heritage up to that point.
Born on the planet Hyperkarn in 15 ABY, Rey Palpatine was the daughter of Dathan and Miramir. While their names were lost to history, Rey's father was the cloned son—an artificial genetic strandcast—of the resurrected Darth Sidious, making her the granddaughter of the fallen Galactic Emperor and Dark Lord of the Sith.
