Sigma/Mega Man X5

Sigma is the final boss from Mega Man X5, a malicious Reploid that is the source of all recent disasters, including scattering the Sigma Virus around Earth and the fall of Eurasia, with the Zero Space and Zero Virus appearing where it crashed. He appears in the last Zero Space stage for a final battle against X or Zero.

First form
After the battle between X and Zero, the winner goes after Sigma, facing him in his new body, dubbed Psycho Sigma (サイコシグマ). He initially wears a cape with multiple energy tethers as well as shoulder plates, although he discards it immediately prior to confronting X and/or Zero. Psycho Sigma largely uses similar maneuvers as in the first fight against him in Mega Man X, only using destructive waves instead of his laser sword. This form is weak to X's Tri-Thunder and Zero's E-Blade.

Attacks:


 * Dash Tackle - Sigma dashes and moves up and down the walls as if wall kicking.
 * Hell Spark - Sigma launches spheres.
 * Hell Blade - Sigma releases a large wave.
 * Sigma can also generate Sigma Viruses that rotate around his body to protect him.

Second form
After his defeat, Sigma appears with a gargantuan body named Final Sigma W (ファイナルシグマW). It is incomplete, and although only the upper half is seen, it is still a very powerful body, giving trouble to the tired Maverick Hunters. It is speculated that this body may have been made by Dr. Wily due to the W on the name and Sigma's quotes after his first form is defeated. This form can only be damaged by hitting the red core on his forehead, and he can't be harmed when he takes a wireframe appearance. He is weak to X's Spike Ball and Zero's Twin Dream. His hands can be destroyed, but they return after a while.

Attacks:


 * Missile Punch - Uses the rockets on the hands to punch the target.
 * Rear-end Bomb - Sigma releases four spheres from his forehead that move to the ground than move in the player's direction two times before disappearing.
 * Thunder Attack - Used after losing half of his energy. Sigma releases electricity from his fingers.
 * Purple Cube Attack - Used after losing half of his energy. Materializes purple cubes in the player's position.
 * Charge Shot - Sigma releases spehres from the palm of his hands.

After his defeat, Sigma turns into "Slime Sigma" (スライムシグマ), attempting one final attack against the Maverick Hunters. Sigma releases a beam from his mouth that pierces the two Hunters, but before falling, Zero takes him down with a shot. He is never directly fought in this form, due to it being a cutscene.

Damage Data Chart

 * Mega Man X5 Damage Data Chart (X)
 * Mega Man X5 Damage Data Chart (Zero)

Other appearances

 * Sigma in his Psycho and Slime forms appear in the opening of Mega Man X6, owing to it recapping the events of Mega Man X5.
 * Psycho Sigma is fought alongside Zero Nightmare in stage 6-3 from the X Challenge mode in Mega Man X Legacy Collection 2.
 * Psycho Sigma is a skin for Sigma in Marvel vs. Capcom: Infinite.
 * In Rockman X DiVE, Final Sigma W appeared as the boss from the fourth Boss Raid on February 2021.

Other media
Psycho Sigma appeared in Rockman X5 IF and Rockman X5.

Trivia

 * This is one of two incarnations of Sigma to share his first boss background music with another portion of the game, the other being the the one from Mega Man X6. In this case, he shares the BGM theme with Sigma Head, and to a lesser extent the post-fight cutscene of said boss fight.
 * Except for the color of the ear parts, the design of Final Sigma W's head is the same as Sigma Head, including the thrusters in the back, suggesting that the developers used the same model for both bosses.