Sigma Virus

The Sigma Virus (シグマウィルス) is the commonly used form of Sigma after Mega Man X2, and the name is also used to refer to his Maverick Virus from the Mega Man X series that turns Reploids into Mavericks.

Brief story
Not much is revealed about the different viruses in the series. Zero was the first Reploid to hold a "Maverick Virus" (It's speculated that Wily created this virus, by analyzing the Evil Energy.), but it technically doesn't turn him in a Maverick, as he was already created with a evil personality by Dr. Wily.

Several years after his creation, Zero is found by the Maverick Hunter Sigma, which fights against Zero and a unknown amount of the virus passed to him, merging with his DNA and becoming later the "Sigma Virus", Sigma himself also becoming a virus. After being repaired by the Maverick Hunters, Zero had no memories of his evil self and became good. Through, Zero was unaware that he holds this virus (possibly weakened after the fight against Sigma), and scattered it throughout the world during his missions as a Maverick Hunter.

In Mega Man X5, Zero notices he is immune to the Sigma Virus, which makes him stronger instead of affecting him. Sigma spread the Sigma Virus through the world to make Zero absorb a large quantity of it, to reactivate Zero's original self dormant inside him. It was also said by Alia that the Sigma Virus outbreak was affecting the humans, implying that the Sigma Virus could even infect biological organisms such as Humans.

Later, Gate was able to revive Sigma in Mega Man X6, but he was not complete and attacked Gate, saying he could revive without his help. In one of the endings from Mega Man X6, Zero acknowledge he was the original carrier of the virus, and allowed himself to be sealed for over 100 years to be studied by a research facility to create a cure to the virus, leading to the end of the virus and the Maverick wars years later.

Mega Man X2
In Mega Man X2, the Sigma Virus is the final boss, a 3D wire frame head of Sigma that can only be harmed by a charged shot, Strike Chain or Shoryuken. It doesn't have health for a final boss, and damage can only be determined by the color of its appearance (green for default, red for critical). It attacks by releasing laser from his eyes and making two enemies appear randomly from his mouth, the enemies being Tubamail-S, Tiranos, Scriver and Fishern. After losing some health, he will also warp around X's current location to hold him, and when successful will cause damage to him until he escapes.

Mega Man X3
In Mega Man X3, Sigma attempts to possess X's body after his defeat, as the bodies he used where not strong enough to defeat X. However, the vaccine created by Dr. Doppler weakened him and X was able to escape.



Mega Man X5
In Mega Man X5, Sigma spreads the Sigma Virus through the world, and it appears as an enemy that looks like a purple Sigma head. If X gets hit with it several times, he will get a condition that damages him for a while. If Zero gets it, he actually becomes stronger (mainly because he is the original bearer of the virus). It can only be destroyed by the player if the part Virus Buster is equipped, or by Zero's saber when using his secret armor.

Zero Virus
Zero Virus (ゼロウィルス) is a powerful virus created by Sigma by combining the Sigma Virus and the virus in the space colony Eurasia in Mega Man X5. It appears as an enemy in the final stages, a purple virus that looks like Zero. When it appeared, it will try to infect the player. If it miss one time, it will reappeared again and try the same way. The Zero Virus is two times more powerful than the Sigma Virus.

It's believed it was created to be like the original form of the Maverick Virus, that was carried by Zero before it infected Sigma.

