Duelling with the Sith Lord Darth Sidious was a very different experience to fighting Dooku. Yoda was almost overwhelmed by the sheer hatred and fury of the Emperor.
--Fact File
Wheless' team worked out three key poses to tell the story:
1) Yoda and Darth Sidious lock lightsabers
2) Yoda is forced back by Sidious' power, and grimaces in pain
3) Yoda uses all of his strength to push Sidious back
[...]
"The shot is only three seconds long, but it communicates to the audience that Yoda has met his match," he says.
--Insider #86: Yoda’s Right Arm
Inside the spacious interior of the Galactic Senate chamber, Yoda challenged the Emperor. The two engaged in a spectacular duel—a contest between the most powerful practitioners of the Force’s Light and Dark Sides. The Emperor proved too powerful to defeat. Although Yoda held his own for much of the duel, in the end the Sith bested him. He realized that continuing to directly confront Palpatine would mean failure. Defeated, Yoda slunk away into the shadow's of the Senate chamber's cavernous depths, leaping into a waiting getaway speeder piloted by Bail Organa.
--The Complete Star Wars Encyclopedia
Yoda went after Palpatine in the empty Senate chamber, but could not defeat the most powerful Sith Lord in history.
--The New Essential Chronology
His true criminal colors revealed after Order 66 wipes out the Jedi Order on a galactic scale, Chancellor Palpatine accepts the title of Darth Sidious and all that goes with it. Reveling in his power, he is challenged by a feisty Yoda in the empty Coruscant Senate chamber. It’s a furious, unprecedented battle royale, with both adversaries hurling and dodging chamber pods. Ultimately, an overmatched Yoda flees to fight another day.
--Star Wars Trading Card Game
Though Yoda is a tough combatant, the Emperor uses his Sith powers to release lightning bolts and hurl floating platforms at his foe. Ultimately the battle proves too much for Yoda, who barely escapes and is whisked away to safety by Senator Bail Organa.
--Ultimate Star Wars
Yoda confronted Sidious in the heart of the Senate chambers. This erupted into an intense duel between these masters of the Force, a fight that Yoda ultimately lost and was forced to flee.
--Databank: Yoda
Master Yoda made a last-ditch attempt to stop him, and their fight spilled over into the now-empty Senate rotunda. Darth Sidious overwhelmed Master Yoda with the destructive energy of the dark side, and the Jedi Master fled Coruscant.
--Databank: Emperor Palpatine/Darth Sidious
Yoda is eventually outmatched by Sidious.
--Revenge of the Sith Story Gallery
The Jedi Master and the Sith Lord dueled in the Senate chamber, but Sidious was too strong for Yoda to defeat.
--Coruscant History Gallery
A fierce duel commenced. Yoda and Darth Sidious each used his side of the Force to try to defeat the other. But the Sith Lord's powers were too strong.
--Revenge of the Sith Canon Junior Novelization
Even the greatest warriors of the Jedi - Mace Windu, Kit Fisto, even Yoda - could not defeat the Sith.
--The Last of the Jedi: Underworld
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