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"Repliforce are the fools this time! Now, all that's left is to destroy Earth with the very weapon they made!"

Sigma is the final boss from Mega Man X4. While the Maverick Hunters and the Repliforce were busy fighting each other, Sigma took control of the Final Weapon and planned to use it on Earth, forcing X or Zero and the General to stop fighting in order to stop the Final Weapon before it could be used.

First form

Sigma is revealed as the true mastermind behind the battles and fights against X or Zero himself. Sigma's appearance is hidden by a cloak and he is armed with a beam scythe, resembling a Grim Reaper. This form can only be damaged by X's Rising Fire or Zero's Ryuenjin.

Reaper Sigma

Sigma using his Shot Attack.

Sigma is constantly appearing and disappearing, and attacks by swinging his large scythe or firing several projectiles that crawl the ground. The projectiles can be avoided by jumping over them. When he appears in the corner of the room, he will use a scythe attack that covers most of the room. It can be avoided by using Wall Kicks on the opposite wall. The best moment to attack Sigma is as soon as he appears.


  • Shot Attack (ショット攻撃) - Sigma releases projectiles that are either shot towards the ground and spread outwards or are immediately spread outwards then moves across the ground.
  • Scythe Attack (鎌攻撃) - Swipes the area with his scythe. This can be dodged by quickly scaling one of the walls, as Sigma will always appear the opposite side of the arena where the player is facing e.g if the player is on the right, then Sigma will appear on the left, and vice versa.

Second form

Reaper Sigma 2

After taking enough damage, Sigma's cloak is burned out, revealing his new body. Although this is the same body, Sigma recoves his health and changes his attack pattern.

Sigma starts by using Scythe Throw, making his scythe spin around him. Afterwards he uses Laser Attack, throwing the scythe on the player's current position. His following attack depends on where the scythe lands: Boomerang Attack if the scythe hits the floor, and Laser Eye if it hits a wall. He then repeats his pattern. A good strategy against him is to stay close to a wall to avoid his attacks and make the scythe hit the wall. When Sigma prepares to use his Laser Eye, dash jump to the wall behind him and attack him from the wall while he is using the attack.


  • Scythe Throw (鎌投げ) - Sigma throws his scythe and it spins around him.
  • Laser Attack (レーザー攻撃) - Sigma throws his scythe in the player's direction. After hitting a surface it will release laser beams across the surface.
  • Boomerang Attack (ブーメラン攻撃) - If the scythe hits the floor, Sigma releases four boomerangs from his shoulders. They track the player, then fly offscreen.
    Reaper Sigma 3

    The (very small) safespot that can be used to dodge Sigma's Laser Eye attack.

    • Laser Eye (レーザーアイ) - If the scythe hits a wall, Sigma fires lasers from his eyes, covering most of the terrain. However, there is a very small space just between Sigma and the wall where the player can just stay here to dodge the attack. Just make sure to jump out afterwards, as the act of Sigma finishing the attack can damage the player

Third form

In his final form, Sigma controls multiple bodies. He has two main bodies named Gunner Sigma (シグマガンナー Sigma Gunner)[1] and Earth Sigma (アースシグマ)[1] and mini bodies shaped like his head. He constantly changes between forms, following the pattern of attacking with the mini bodies, Gunner Sigma, mini bodies, and Earth Sigma.

Mini Bodies


Three metallic objects resembling Sigma's head, each with an element. The red head releases fireballs, the yellow head electricity, and the blue head has a freezing breath.


  • Flame Bullet (炎弾) - The red head fires four sets of fireballs, at the player's position.
  • Electromagnetic Bullet (電磁弾) - The yellow head releases six spheres from its forehead, with split into electric currents after hitting a surface.
  • Ice Fog (氷霧) - The blue head releases a cold fog from its mouth. It covers most of the ground.

Earth Sigma

Earth Sigma

Earth Sigma is the body that appears on the bottom left of the room. It is a giant disfigured head of Sigma.


  • Spike Attack (トゲ攻撃) - When Earth Sigma appears, spikes appear on the right wall and Earth Sigma attempts to push the player to them.
  • Slime Body (スライムボディ) - Earth Sigma starts sucking debris, also pulling the player, and releases the debris. Quite a difficult attack to dodge,as there is a lot of it to avoid.

Gunner Sigma

Gunner Sigma

Gunner Sigma using Tracking Laser.

Gunner Sigma is an armed cyborg-like body that appears on the top right of the room.


  • Clear Laser (薙ぎ払いレーザー) - Gunner Sigma fires a laser beam that covers the whole floor.
  • Tracking Laser (追尾レーザー) - Gunner Sigma fires a laser beam on the player's direction.

Damage Data Chart


X-Buster Lightning Web Soul Body Aiming Laser Double Cyclone Rising Fire Frost Tower Ground Hunter Twin Slasher Nova Strike
1st Phase 0:0:0 0:0 0:0 0:0 0:0 6:4+ 0:0 0:0 0:0 0
2nd Phase 1:2:3 4:4+ 0:1+ 0:0 0:0 0:0 0:0 0:0 0:0 6
Earth Sigma 0:0:2 0:0 0:0 0:0 0:0 0:0 0:0 2:3 0:0 4
Gunner Sigma 0:1:2 0:0 3:0 0:0 0:0 0:0 0:0 0:0 0:0 4



Special Techniques

First Slash Second Slash Third Slash Wall Slash Kuuenzan Raijingeki Ryuenjin Hyouretsuzan Shippuuga Rakuhouha
1st Phase -- -- -- -- 0 -- 6 0 -- 0
2nd Phase 1 1 3 1 3 3 0 2 1 4
Earth Sigma 1 1 2 2 2 0 0 3 2 0
Gunner Sigma -- -- -- 2 3 -- 4 2 -- 1


  • For X-Buster, the first number is damage done with standard, uncharged shots; the second is damage done when the weapon is charged a bit; third number is damage done when it is fully charged.
    • A fully-charged X-Buster shot does the same damage in all of its forms (normal Charge Shot, Stock Shot, and Plasma Shot).
    • Any subsequent damage inflicted after the Plasma Shot's initial blast is 1 unit per hit.
  • For the eight Special Weapons, the first number is damage done when the weapon is used in normal fire; the second is when the weapon is used in its charged state.
  • For Special Weapons that are capable of striking more than once, damage values on this chart are listed according to how much a weapon inflicts per hit, not the total amount of damage done. Those that do strike more than once will be marked with a plus sign.
  • For Soul Body, the first number is damage done with the hologram, and the second number is damage inflicted with the buster shots fired from the solid hologram; the solid hologram itself cannot inflict damage to Sigma.




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