4. The Eight Inner Gates
The Eight Inner Gates is a very powerful ability. They are basically chakra limiters that are placed all over the body, in order to minimize power usage, and damage to the body. Training allows a person to remove these limiters, and hence access its powers. Might Guy demonstrated it’s full power during the Fourth Great Ninja War against Madara Uchiha. He absolutely destroyed Madara with this, even though at that time Madara was in Ten Tails Jinchuuriki form. If one uses Al 8 Gates, their body turns to ash afterwards. Like Might Duy, who used it to attack Seven Swordsmen and almost killed all of them. Guy was saved by Naruto otherwise he would have died as well.
Sharingan is the Kekkei Genkai ability of the Uchiha Clan. It allows the user to see the chakra pathway, and the ability to copy the opponents techniques, except the bloodline limit techniques, and see through Ninjutsu, Genjutsu, and Taijutsu as well. This is a very underrated ability.
Kakashi Hatake has copied more than a thousand jutsu with his Sharingan. Mangekyou Sharingan and Eternal Mangekyou Sharingan are the next level forms of sharingan. Their ability can destroy the opponent in just one look like Amaterasu. It surely makes it one of the overpowered abilities.