Yellow Devil MK-II

Yellow Devil MK-II (イエローデビル Ｍｋ－Ⅱ) is a powered up version of the Yellow Devil that appears as the boss of the second Wily Castle stage from Mega Man 3.

Yellow Devil MK-II attacks by splitting itself into parts and moving them fast to the other side of the room, hitting the opponent in the way of the parts and reassembling after all parts reach the other side. When it moves to the right by the first time when entering the room and moves to the left, it splits into 24 parts that move one at time from one side to the other. When moving to the right side for the second time onward, he combines into five parts that bounce to the other side. When assembled, his eye appears and shots at Mega Man three times before moving to other side. Like the original Yellow Devil, he can only be damage on the eye. He is weak to the Hard Knuckle. Shadow Blade also does considerable damage to him, and as its speed is higher that the Hard Knuckle, it can be used to defeat Yellow Devil MK-II earlier.

Mega Man Megamix
Yellow Devil MK-II appears in the story Metal Heart from the manga Mega Man Megamix and Rockman Remix. In the manga, his body was created by Dr. Wily and can take any shape, but his brain was taken from a broken toy robot that Wily found in a junkyard. All he can say is sounds with the letter "M".

When MK-II was activated, he didn't obey Wily and left his hideout. Wily orders his Robot Masters from Mega Man 3 to bring him back, and if not possible, destroy him. They fight against Yellow Devil MK-II in the streets, and it calls the attention of the population. Dr. Light and some of his robots where in the same city for the party commemorating the installation of the new Mother Computer, and they notice the commotion. Mega Man goes to the local and joins the Mega Man 3 Robot Masters to stop Yellow Devil MK-II, and it is scared when Mega Man attacked near his head, digging a tunnel underground to escape and going out of sight.

The party moved to the central control building to see if the Mother Computer can locate the Yellow Devil, and once there, it suddenly appears in front of them and moves upstairs. Mega Man and Shadow Man manage to follow him, but the other are left behind by the building's security system. Mega Man and Shadow Man battle against the Yellow Devil while its moving up, and Shadow Man is damaged near the Mother Computer's room. Dr. Light noticed the security system was acting strange, as it closed to them and not for the intruder. Light asks Auto to access the Mother Computer, and discovers it is emitting a "SON" signal, which he doesn't understanding. He them asks Roll to search for data about the Mother Computer's previous job, and discovers the Mother Computer used to be the main control computer of a toy company. Wily says he used the brain of a toy robot he had found, and Light notices SON is actually the English word son (the manga was originally released in Japanese), and the Yellow Devil is actually a kid trying to see his mother. They ask Mega Man to stop attacking him. However, Shadow Man was not able to hear them and remembered Wily's orders, attacking the Yellow Devil's eye with a Shadow Blade before collapsing to destroy it, also hitting the Mother Computer with the attack, cutting the energy of the city.

Because of the damage, the Mother Computer could no longer be used as a Mother Computer, and the old one was placed back. Dr. Light repaired the new Mother Computer and the toy robot's brain, and placed them together as the control computer of a park.

Trivia
Some fans believe the Yellow Devil MK-II to be female because the two bulges below its eye resemble breasts.