Palpatine explains that Plagueis was so powerful and wise, he had mastered the dark side of the Force to such an extent that he could cheat death and create life; unnatural abilities which are unknown to the Jedi.
Sidious later recounted the tale of his master's demise to lure the Jedi Knight Anakin Skywalker to the dark side of the Force, calling the fallen Sith Lord Darth Plagueis the Wise. After his own demise, Sidious used his master's teachings to cheat death, though true immortality still eluded him up until his final end.
In addition, after killing Mace Windu, Anakin is committed to following Sidious; he has little choice but to do as Sidious says and hope to be rewarded with the knowledge he wants. Well, Palpatine did actually know how to cheat death. He did so after his apprentice body slammed him into the abyss.
Why Qui-Gon Jinn Was Palpatine's Greatest Threat. Unlike Yoda and the Jedi High Council, Qui-Gon Jinn was only concerned about the will of the Force. Therefore, Palpatine needed Qui-Gonn out of the way because he was better connected to the Force than the other Jedi.
Supreme Chancellor : Be careful of the Jedi, Anakin. Only through me can you achieve a power greater than any Jedi. Learn to know the Dark Side of the Force and you will be able to save your wife from certain death.
A recent survey of Star Wars fans found that the most popular Palpatine quote is “Do it,” which he famously says to Anakin Skywalker in Revenge of the Sith, followed by “Unlimited power!” from the same scene.
1 "There is no mercy."
Having soundly defeated his former apprentice Maul, the Dathormian pleads Sidious to show mercy, but the Dark Lord replies "There is no mercy," before unleashing his usual method of torture.
Palpatine admits to Darth Vader that the Jedi he actually feared most was none other than Jocasta Nu.
As powerful as Darth Sidious may have been, it's easy to forget he actually seemed afraid of Master Yoda.
We are just barely seeing a 600-something-year-old Yoda in the High Republic era. And given that Qui-Gon Jinn dies in 32 BBY, a fight beyond that point would be pointless since, as a Jedi spirit, Jinn would arguably be stronger than the still physically alive Yoda.
Emperor Vitiate was a Sith Lord who successfully gained near immortality by draining the life force of an entire planet, later attempting to drain all life in the galaxy, which would give him true immortality.
1 Darth Sidious
As well as being a gifted bladesman Sidious' connection to the Dark Side is extremely powerful, granting Sidious the ability to conduct force lightning.
In non-canon material it is said that Palpatine had a number of concubines and never took a wife in fear that he would produce a legitimate heir. One of these non-canon concubines was Roganda Ismaren, a former Jedi who survived Order 66, and lived for a time at Palpatine's side.
Eventually, Sion was struck down, but he did not die. Instead, the pain within him welled up to agonizing levels, driving Sion to rise once more and strike down his would-be killer with all his anger and hate. Sion found that he could hold his own decomposing body together with the dark side of the Force.
Darth Vectivus was created by Aaron Allston for the first novel of the Star Wars: Legacy of the Force series, Legacy of the Force: Betrayal. He appeared as a spirit to Nelani Dinn and served as a platform for Lumiya to convince Jacen Solo to become Darth Caedus by showing him that not all Sith were necessarily evil.
Vectivus ended up dying peacefully with loved ones at his side. He was one of the few Sith Lords to enjoy such a privilege.
In truth, the Sith normally wielded enough powers to fight without a lightsaber, but every apprentice still learned to use one as part of his or her training. Sidious himself felt that he and his peers had outgrown the use of lightsabers, and only continued carrying them to mock the Jedi.
If Obi-Wan had fought Sidious, he would have died. That has been well established, but I think Yoda was more concerned with the fact that Obi-Wan needed to face Anakin. Yoda wasn't sure if he could even beat Sidious, but he knew he could keep Sidious distracted from their fight.
Anakin Skywalker could have thwarted Darth Sidious and in fact did, albeit almost 25 years after he was given the initial opportunity. Anakin fell into Sidious' trap and attacked Windu, as Sidious played victim, only to then spring to life and fire lightning upon Windu.
Even after his brutal scorching in the fires of Mustafar, sand remained the only natural phenomenon that Vader feared. To him, sand was a reminder that he'd failed to save his mother or Padme from death.
Using his influence over the Trade Federation, Sidious orchestrated the blockade and invasion of his homeworld. His goal was to generate sympathy for the people of Naboo in order to become the next Supreme Chancellor.
The Emperor : [laughing] Perhaps you refer to the imminent attack of your rebel fleet? Yes, I assure you, we are quite safe from your friends here. Luke : Your overconfidence is your weakness. The Emperor : Your faith in your friends is yours!
He's incredibly intelligent, cunning, and manipulative in ways no other Sith Lord was/is. Most others were driven by pure vengeance and/or anger, but Sidious was driven by a primal instinct to survive and gain power. 160–190 would be around the range which I would estimate his IQ to be.