If Yoda had turned to the dark side in Star Wars, he would have eclipsed the might of even the strongest Sith Master, Emporer Palpatine. Each Jedi at some point comes face-to-face with the dark side of the force. Most turn away from it and continue down the lighter path, yet many still succumb to the pull of evil. Yoda was no exception to this, and had to confront the possibility of the dark within him on multiple occasions throughout his 900-year life.
Sheev Palpatine, also known as Darth Sidious, was a Dark Lord of the Sith and the Emperor of the Galactic Empire. No force wielder in the galaxy could match his hateful connection to the dark side, and the power it allowed him to exhibit. Yoda and Palpatine once engaged in a skirmish on Coruscant during the events of Star Wars: Revenge of the Sith, until the evenly matched duel ended in Yoda retreating. Palpatine proved in that confrontation that, with his use of the dark side, he was able to best the Jedi Grand Master.
However, if Yoda had become a dark force , it would have been absolutely terrifying. Dooku, who knew both Yoda and Palpatine very well, confirmed this. Already a close match for Palpatine, a version of Yoda that lacked the Jedi way of restraint could have inflicted serious damage. If Yoda had let go of discipline, and instead lashed out with the force abilities that only the Sith possess, Palpatine wouldn't have stood a chance.
Count Dooku was once Yoda's student, and the reason that Yoda later refused to train Luke. When Dooku became Palpatine's apprentice, he attempted to sway Yoda to the dark side as well. Recorded in the book Dark Rendezvous, Dooku approached Yoda with a proposition. As he tried to persuade his old master, Dooku realized how "foolish he had been" and saw that "If Yoda ever turned that way, Sidious himself would be annihilated. The universe had yet to comprehend the kind of evil that a Jedi Knight of nearly nine hundred years could wield." Dooku recognized in that moment that a Sith Yoda would have been unstoppable.
When a force chooses to follow the light side, they also choose to abide by a strict set of codes. This does not apply to the Sith, so there are many force powers that only Sith can use. Along with force lightning and force choke, there is also the brutal force rage. If Yoda had been able to use these powers in combat, he would've been extremely difficult to beat. With the connection that Yoda had to the force, the impact of him using dark side powers would mean unparalleled destruction.
Yoda was one of the wisest masters of the Jedi Order, yet even he was tempted by the dark side. If he had ed the ranks of the Sith, the events of Star Wars would have played out very differently. He could have toppled Palpatine's reign and claimed the Empire for himself. Yoda used his power in the force to restore peace across many worlds, and he was respected for his comion. However, if he had chosen the Sith existence of hate and evil, he would have been the most feared being in the galaxy.
