During the time of the Clone Wars, Mace Windu was regarded as one the greatest lightsaber duelists of all time. He utilized the extremely rare Lightsaber form known as Vapaad, which allowed him to leech an enemy’s force power if they used the dark side, directing it back against them. But over his time as a Master, there was one person that Windu refused to ever fight in single combat. General Grievous. Why was this?
On the opposite side of the war to Mace Windu was General Grievous, a fierce Kaleesh warlord who became so renowned on his homeworld that they made him a demi-god. His life took a sharp turn though when Count Dooku blew up his ship mid flight, causing him to be horrifically injured. This led to Dooku implanting Grievous with highly advanced cybernetics that allowed him to mimic the force powers of a Jedi. One of these cyberntics was implanted into his brain, giving him absolutely crazy reaction times, and the ability to recognize any lightsaber form the moment someone started using it. The cybernetics in his brain were so advanced that they even allowed him to replicate the lightsaber form immediately, despite never having used it.
Now knowing this, Mace Windu was worried but still confident that his extreme strength in the force and completely unique Lightsaber form, Vapaad, would be enough to take the cyborg General down if worst came to worse. Unfortunately though, Windu was dead wrong. When the two finally fought eachother, Mace severely underestimated Grievous’ brain. Windu started the fight by utilizing his Vapaad technique, hoping to overwhelm the cyborg with sheer strenght and power. To his absolutely shock though, Grievous began to mimic his use of Vapaad almost instantly, and began to overpower the Jedi Master.