The Mangekyou Sharingan in Naruto is an evolved form of the Sharingan, which can be awakened by a user upon experiencing great emotional trauma, usually triggered by the tragic death of a loved one. This eye grants tremendous powers which usually come in two distinct abilities, one in each eye.
Source：https://www.cbr.com/naruto-strongest-weakest-mangekyo-sharingan-users/
