Sigma/Mega Man X6

Sigma is the final boss from Mega Man X6. While he was not fully restored, he is still a threat to the Maverick Hunters, being filled with hatred to them and wanting revenge against X and Zero.

First form
After Gate's defeat, he says that he restored Sigma, with Sigma revealing himself and saying that he didn't need Gate's help to return, attacking Gate and leaving, taunting the Maverick Hunter to come and fight him. After having a rematch with the eight Nightmare Investigators, the Hunter finds Sigma. Due to being incomplete, Sigma's appearance and attacks makes him resembles a zombie. This form is weak to X's Metal Anchor and Zero's Rakukojin.

Attacks:
 * Bug Shot - Sigma shots from his forehead.
 * Bug Cloud - Sigma moves his arm and creates a large vertical energy cloud that moves forward. It can be pushed back with attacks.
 * Bug Wave - Used after losing half of his life energy. Sigma moves his arm and creates a purple wave that flies forward.
 * Counter Shot - When damaged by his weakness or with strong attacks, Sigma falls and drops a harmful purple substance on the ground, and green spheres appear from his body and fly on the player's direction.

Second form
After X or Zero defeat his first form, Sigma emerges as a gigantic unfinished body with a skeletal appearance named Hell Sigma (ヘルシグマ). This form can only be damaged when the mouth is open. He is weak to Ground Dash and Magma Blade with X, and to Ensuizan and Sentsuizan with Zero.

Attacks:
 * Enemy Summon - Sigma will constantly release green spheres from his forehead that take the shape of a slime-like Sigma heads, which will do one of the three actions below. They are like enemies, and may drop items like Life Energy and Weapon Energy on the normal difficulty. They drop nothing on hard. They have low health and are destroyed by the other attacks used by Sigma.
 * The head falls on the floor and slowly crawls on the player's direction.
 * The head hovers up and down while attacking with shots from the mouth.
 * The head take the shape of a spiked platform in the air and moves left and right, occasionally going down to pierce the player. If the player stands on it for a while, it will reverte its shape, trying to pierce upward.
 * Giant Laser - Sigma opens his mouth and releases a giant laser, covering most of the area in front of him. It can be avoided by crouching under the mouth.
 * Beam Attack - Sigma opens his mouth and a lock-on target appears on the floor, a laser appearing vertically on the marked position shortly after.
 * Projectile Attack - Sigma releases a small energy sphere from his mouth to the left corner of the room, which quickly grows and moves away to the right. If released straight forward, it can be avoided by crouching. If released diagonally, the player can hover or double jump to dodge it.

Damage Data Chart

 * Mega Man X6 Damage Data Chart (X)
 * Mega Man X6 Damage Data Chart (Zero)

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Trivia

 * While the player only fights this "incomplete" form of Sigma in Mega Man X6, Sigma used a similar-looking form in the ending cinematic for Mega Man X7, which is presumably an unfinished spare body or what was left of his first form.