Star Wars: The Dark Jedi Power Mace Windu Used To Beat Palpatine Explained
Mace Windu is typically near the top on fans' lists of the most powerful or beloved Jedis. Brought to life by Samuel L. Jackson in the prequel trilogy, he was considered a champion of the Jedi as one of the most powerful in existence and perhaps the greatest lightsaber duelist the Jedi Order ever produced. That status is possible partly because of his ability to best the most dangerous Sith of his time in Emperor Palpatine/Darth Sidious (Ian McDiarmid), and through Vaapad, which is the dark Jedi power he used to accomplish the feat.
The discipline known as Vaapad is the seventh recognized by the Jedi Order. It differs from the others in some intense ways, namely that the user would incorporate brutal attacks on their opponent and even channel Dark Side energy to allow themselves to become even more powerful. Windu's ability to master this discipline (one he created and therefore making him the only living master) made it possible for him to do what no other Jedi could and defeat the Sith Master, Darth Sidious.
The discipline is named for a multi-tentacled creature that moved quickly, with users wielding their lightsabers in such a way that their quick movements made it seem like they were using more than one. While it made the user extremely powerful and a formidable force to be reckoned with, it also demanded a high price, one that less disciplined Jedi would have a hard time paying; they would have to skirt the Dark Side.
The user has to relish combat
If a Jedi wants to remain pure in heart and therefore strong against the Dark Side of the Force, they must follow some fundamental rules. They cannot form emotional attachments, as we have seen an example of such with Anakin Skywalker. They also must remain selfless; willing to serve and follow the Jedi Code of Conduct. The Code states that a Jedi must use their power to defend and protect, never to attack others. With that in mind, the form of Vaapad contradicts the rules.
Users of Vaapad are taught to relish the fight. They give themselves over as a conduit to their opponent's rage and hatred, acting as one-half of a loop of energy. They not only relish in the fight but also find great satisfaction in the victory, which plays to vanity, ambition, and many other characteristics that could prove dangerous for a Jedi. Think about Anakin's feelings that he could be a much more powerful Jedi if Obi-Wan wasn't holding him back. Vaapad forces the user to give himself over to the exposure to these negative emotions and use them to their advantage. And while that seems dangerous, Mace Windu is the perfect Jedi to master this discipline, as he has never been one to shy away from the Dark Side.
Mace always came dangerously close to the Dark Side
Mace Windu is a strong Jedi who displays a lot of hesitation when it comes to Anakin Skywalker. He seems to be strong in the Force and someone others would lean on or follow. That makes it hard to fathom that he wouldn't strictly adhere to what the Jedi Council preaches. But then again, he has always been an outlier. While the others all carry blue or green lightsabers, Windu carries purple. What makes that little tidbit even more compelling is that purple combines blue and red. Combining the blue color of the Jedi with the red lightsaber color of the Sith creates the purple and symbolizes the bridge between the two.
In the novelization of "Star Wars: Return of the Sith," Windu explains to Obi-Wan why Vaapad works and why flirting with the Dark Side is less dangerous for him. "I created Vaapad to answer my weakness: it channels my own darkness into a weapon of the light." He admits to the younger Jedi that his own darkness within, the weaknesses that the Dark Side feeds upon, is the weapon he leans on to fight for the light. He explains that Yoda's discipline is also an answer to his weaknesses, meaning his age and stature.
This explains how he could relish in battle and the satisfaction of victory, and how he can employ brutal attacks when Jedi are meant to protect and defend. He becomes a conundrum as he uses everything the Dark Side feeds upon to become stronger in the Light Side of the Force.