I agree, only extremely skilled Uchiha such as himself contain techniques like Inzanami, Inzanagi, and his main move Kotoamatsukami, which is regarded as a genjutsu of the highest class. It literally controls a persons mind, and body by making them believe they are experiencing something they're not. This is the technique everybody wanted. From Danzo, to Itachi, and even Obito. This technique could have literally turned Sasuke into a good guy, and make him believe his clan was never murdered by the orders of the Hokage, or even ever murdered at all. I believe Shisui was the best of his clan in Genjutsu, he even possessed the Body Flicker Technique, which is similar to the Thunder God Technique. He was probably the strongest of his clan, just under Madara, Obito, and I believe he even rivals with Itachi. At the point Sasuke's at now, and before the time of his death I believe he would be above Sasuke as far as skills go, though I can't state this as a fact, it's my opinion. To pocess the Mangekyō Sharingan, and have his level of Genjutsu he obviously had to have been extremely powerful. He's no ordinary Uchiha.The only reason I believe he wasn't above Itachi is because if he was he wouldn't have given him his eye. He would've helped defeat the clan. Obviously before his death he was stronger, but I think he knew Itachi pocessed the capability of surpassing him. Otherwise he would've kept the one eye he had left.
EDIT: Tsukiyumi was nothing compared to Shisui's Kotoamatsukami, otherwise Obito would've taken Itachi's eyes to get Tsukiyumi. Who's eyes did Obito want more than any bodies, Shisui's, because he knew this was the most powerful Genjutsu, right under Tsuki-no Yumi, or the Eye of the Moon Genjutsu.
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