During his life Shisui received praise as the most gifted genjutsu user of the Uchiha clan of his generation and their most powerful member, his ocular powers even surpassed that of Itachi Uchiha, whom Shisui mentored and they thought of each other as brothers.
With Itachi's odd behavior, was tasked with keeping an eye on him. Itachi was very important to the clan's plan for a takeover given his close position to the Hokage and the elders. Unknown to the Uchiha clan, Shisui and Itachi both disagreed with the takeover and sought alternatives, Shisui was going to use his Koto Amatsukami to force peace. Danzo thought it would be a wasted effort, and became paranoid; if Shisui was willing to use his jutsu against his own clan, then would he be willing to use it against the Hokage and the elders? Danzo attacked Shisui and managed to take Shisui's right eye, but Shisui managed to find Itachi and tell him what happened, he then asked Itachi to help him fake his suicide and entrusted Itachi with his left eye.
Jutsus: Shisui possessed the Uchihas' infamous Sharingan, which permitted the perception of an individual's chakra along with increased sensitivity to movement, photographic reflexes, and a hypnotic gaze.
Shisui possessed the ability to use the Uchihas' secret fire jutsus, such as Grand Fireball which manifests as a gigantic ball of flame and Phoenix Flowers which forms a flurry of small fireballs, amongst others, and Halo Dance which would release waves of fire from his weapon. He also made use of crow summons that he deployed in combat as well.
Shisui was particularly known for his mastery of the academy-level jutsu Body Flicker. Normally a jutsu used for quick entrances or escapes, he combined the high rate of speed with his Sharingan's superior vision to successfully use it during battle.
Mangekyou Sharingan; Shisui's Mangekyou Sharingan possessed a genjutsu of the highest caliber, called Koto Amatsukami. This technique could implant thoughts or ideas into peoples' subconscious which they would consciously act upon as if it were their own, completely unaware that they are being manipulated. It's so powerful that it can even overpower other forms of control. Unfortunately it takes time for the eye to recuperate after use so it cannot be used in quick succession.
Using the power of both eyes at the same time, Shisui was also able to manifest Susanoo, a humanoid energy construct. It boasts great strength and endurance, protecting him while simultaneously fighting on his behalf. It's equipped with a drill-like sword and is able to spray a barrage of energy spikes. A downside to this formidable ability is that it tears down the user's body during use.