Itachi
Uchiha
Genjutsu (幻術; Literally meaning "Illusionary Techniques") are techniques that are employed in the same fashion as ninjutsu, requiring chakra and hand seals. However, the primary difference between the two is that the effects of genjutsu are illusory; instead of attacking the victim's body, like taijutsu or ninjutsu, genjutsu techniques manipulate the flow of chakra in the victim's brain, thus causing a disruption in their senses. According to the Second Mizukage, genjutsu fittingly falls under the broad category of Yin Release.
This is often used to create false images or to cause pain from trauma (because the body is led to believe it is in pain); however, there are plenty of other uses depending on the situation. They are not used as often as ninjutsu because they don't physically harm the opponent, but several characters have made themselves well-known for their great prowess with genjutsu like Itachi Uchiha, Kurenai Yūhi, the Second Mizukage and Tayuya. Genjutsu can also be used to manipulate others, similar to brainwashing by feeding the victim illusive suggestions, the primary example being Tobi controlling Yagura. However, there exists at least one genjutsu, Izanagi, that has the opposite effects to normal genjutsu, by changing reality to illusion and vice versa. Genjutsu can also be used for other supplementary purposes such as interrogating an individual by breaking their will.
Genjutsu
Demonic Illusion: Mirror Heaven and Earth Change The user decrypts a genjutsu that has been applied onto them and casts back a technique with identical effects onto the opponent. It's a form of illusion reversal, but in order to instantly read through a technique and cast it in return, the Sharingan's power is necessary. As genjutsu is initially used to confuse the enemy, this technique, which sends it right back to its caster, deals a high amount of mental damage, more than anything else.
Demonic Illusion: Shackling Stakes Technique Firstly, this technique requires the use of the Genjutsu: Sharingan. The opponent is caught in the illusionary world created by the user, and the victim is tormented with the sensation of having spikes driven through their limbs, taking away their body's freedom. At the same time, the physical pain accompanying the illusion reveals that the greatest use this technique has is torture.
This genjutsu traps a victim in a powerful illusion with no necessary eye contact; similar to Ephemeral. When used on Naruto, the genjutsu projected a torrent of crows, leaving him at Itachi's mercy.
Itachi seemingly activates this technique by simply pointing at his target. When the technique was used on Naruto Uzumaki, crows flocked from Itachi and turned into shuriken that bombarded him, and then attempted to put him to sleep. When he resisted the sleep command, Naruto then experienced the sensation of his body parts turning into his closest friends who then tortured him psychologically.
Tsukuyomi requires eye contact to be performed, trapping the target within an illusion completely under the user's control. Itachi's prowess with the technique has allowed him to alter the perception of time with ease within the genjutsu to make a few seconds seem like many days as a means to torture the target. This results in the victim suffering psychological trauma that incapacitates them for a considerable period of time.
There are several other jutsus such as these.
Fore there are no limits to his greatness.