Insanity

Insanity is a recurring theme is the Mega Man franchise. Many characters in the series exhibit symptoms of mania or outright insanity, often seeking to cause great harm or destruction to others or the world in the name of their cause. Though these causes are often meant to do good for either humanity or Reploids, the amount of damage it will inflict heavily outweighs the positive changes, and must be stopped. Some individuals, however, seek revenge for something that happened to them or for someone they have lost. Others, such as Vile, are driven to prove their own self-worth, and go to extreme measures to do so.

Original Mega Man series
Dr. Wily was once a man with good intentions; as shown in Mega Man 11, his original vision was to create something that could turn ordinary robots into superheroes by enhancing their powers. Wily attempted to achieve this with the Double Gear System, but Dr. Light, believing that the Double Gear System was too dangerous, got Wily's research on the Double Gear project cancelled while both doctors were still in university. This angered Wily so severely that he ended his friendship with Light and stormed off to prove the world that he was "right all along." Since then, his worldview grew more and more extreme over time; this, combined with the envy Wily developed from constantly being overshadowed by Light's achievements, eventually drove him to attempt to take over the world countless times, even after being defeated by Mega Man time and time again.

Grenade Man is a sadomasochist; he takes pleasure in both receiving pain and inflicting it on others. This is shown prominently during his battle in Mega Man 8; aside from constantly expressing his desire to crush or destroy Mega Man, he also giggles when hit with his weakness, the Thunder Claw, and enthusiastically shouts "Oh yeah!" when hit by one of his own Flash Bombs. He even exclaims "That felt good!" when he's finally defeated.

Burner Man was tricked by King into believing that there was a bomb inside of him that would explode and destroy him unless he burned down a forest every day. This has led to Burner Man becoming a pyromaniac who takes joy in causing environmental destructuon for the sake of warding off the make-believe threat of self-destruction.

Mega Man X series
Sigma originally had a stable grip on his sanity, but he lost it after he went Maverick and his worldview was warped drastically by the Maverick Virus. After fully succumbing to the virus, Sigma adopted the belief that humans are holding Reploids back and must be destroyed in order for Reploids to continue evolving. Acting on this belief, Sigma has made many attempts to destroy humanity, as well as the Maverick Hunters that oppose him. Prior to his defeat in Mega Man X8, Sigma was able to resurrect himself after each defeat, progressively growing more and more deranged the more times he returned from the dead.

Vile suffers from a short circuit in his electronic brain, causing him to be reckless and needlessly violent. These traits, as well as his lust for revenge against his enemies, are shown prominently in all of his appearances in the series. Even though he was a Maverick Hunter, Vile's aggressive nature got him branded as a Maverick due to how much of a danger he was to himself and everyone around him. When Sigma became a Maverick and initiated a revolution against humanity, Vile joined the movement to prove his strength. He was destroyed by X in Mega Man X, but later rebuilt and upgraded by Dr. Doppler in Mega Man X3. Upon being resurrected by the doctor, Vile found that the only thing he could think of was exacting his revenge on X (additionally, the English SNES manual states that Vile was also infected with the Maverick Virus, which further augmented his insanity), and he broke free from Doppler's control to pursue X on his own, only to be destroyed again. Vile returned once more in Mega Man X8 with the same goal in mind, although this time around he also made comments about creating a new world only for new Reploids, as if he were one of the New Generation Reploids.

Double.

Gate.

Lumine.

Certain Mavericks.

Mega Man Zero series
Dr. Weil.

Omega.

Mega Man ZX
Serpent.

Prometheus and Pandora.

Master Albert.

Siarnaq.

Master Thomas.

Mega Man Battle Network series
Lord Wily.

Sean Obihiro.

Speedy Dave.

Anetta.

Dr. Regal.

Mega Man Star Force series
Dr. Vega.

Mega Man cartoon series
Dr. Wily (Ruby-Spears).

MegaMan NT Warrior series
Mr. Wily.

Dr. Regal (anime).

Darkloids.

Domon Atsuki.

Professor (anime).

Mega Man Megamix and Gigamix
Bass (Mega Man Megamix).

Archie Comics
M'egga Man

Sonic Man (Roboticized Master)

Not Mega Man Related
M. Bison

Doctor Eggman

Deadly Six