Nightmare Phenomenon

The Nightmare Phenomenon is a phenomena caused by the Nightmares created by Gate in Mega Man X6, that affect Reploids' DNA data and even the environment. Gate was able to create this by analyzing a piece of Zero's DNA, found by him in the remains of Eurasia.

Characteristics
The Nightmare is an artificial entity shown to take on multiple forms. It can be described as both a virus and as a phenomenon.

The Virus
"I found out what the Nightmare is... The Nightmare is an artificial virus. It infects Reploids and rewrites their DNA and AI programs, immobilizing them. At worst, even their appearance changes. We don't know exactly as our analysis is not yet complete... But it is very similar to the Mavericks."

- Alia, Mega Man X6

The viral form of the Nightmare vaguely resembles a Reploid, disginguished by its black and golden frame, a single large red eye on its head and flexible appendages patterned after DNA chains.

The Nightmare is designed to infect Reploids and immobilize them as it rewrites their DNA and AI programs. During the rewriting process, the Nightmare also inputs a certain code that allows control over the infected Reploid. The victims are modified to the point that even their appearance changes; however, there are cases in which the Reploid does not survive the aggressive intrusion.

The manner in which the Nightmare affects its victims is largely similar to the Sigma Virus; however, while a normal virus usually dies with the host, the Nightmare is strong enough to survive the Reploid's destruction. On the other hand, since its energy is so powerful and concentrated, it can be damaged and even deleted by regular weaponry, without the need of a special vaccine. Upon its destruction, a Nightmare will drop an item called a Nightmare Soul.

Gathering Nightmare Souls increases the player's Hunter Rank, and collecting at least 3000 of those will trigger a cutscene with Alia revealing the true nature of the Nightmare. Dynamo also demonstrates an obssession with gathering Nightmare Souls, expressing a desire of powering up with the DNA within them. Take note that only the first Hunter to achieve this will have his specific cutscene triggered as there are 2 versions of this cutscene available (one for X and one for Zero).

Many of the rescuable Reploids in Mega Man X6 are located dangerously close to the Nightmares, requiring the player to act quickly before the virus latches onto the Reploid's back and rewrites its DNA. Reploids modified by the Nightmare can no longer be rescued; they are lost forever, along with the reward the player would obtain from saving them. The infected Reploid and the Nightmare may still be destroyed, but the Nightmare will not yield a Nightmare Soul in this scenario.

The Phenomenon
"It shows Reploids a kind of "dream" for human beings... no. It's a "Nightmare". The Nightmare makes Reploids confused. In the worst case, they may malfunction or delete themselves."

- Isoc, Mega Man X6

The Nightmare has earned its name for its ability to produce nightmarish visions on Reploids. While advancing through stages in Mega Man X6, players will come across abnormal events that cannot be detected by Alia, indicating the presence of a "Nightmare phenomenon". The Nightmare is said by Isoc to confuse Reploids, leading them to behave erratically or even destroy themselves. Examples of Nightmare phenomena in Mega Man X6 include:

Nightmare Souls
Whenever the player defeats a Nightmare Virus in a level or defeats the Maverick at the end of a level, they will receive a Nightmare Soul. There are 4 types of Nightmare Souls known in this game, they are:
 * Blue Nightmare Soul (Normal): Appears after a Nightmare has been destroyed. Worth 8 souls each.
 * Blue Nightmare Soul (Small): Appears when the Nightmare soul that has just been destroyed has not been obtained after 3 seconds. Worth 4 souls each. If the soul is not obtained after 5 seconds, it will re-spawn into a new Nightmare where destroying it would not generate any Nightmare souls.
 * Green Nightmare Soul: Appears after defeating a Maverick Boss. The Nightmare soul will glow and descend onto the Hunter that is responsible for defeating it. Worth 200 souls each. It can also be obtained from Dynamo in the Secret Boss fights if you hit him twice with his weakness (Meteor Rain or Ensuizan) in which he will drop one of those for you to collect. Dynamo will drop a maximum of 3 such Nightmare Souls per battle, which means you can at least 600 souls if you go into any stage and defeat Dynamo there.
 * Red Nightmare Soul: Appears if you took too long to defeat a Maverick Boss. Upon his defeat this soul will descend onto you instead of the green one. Worth 100 souls each.

If you have passed through a stage obtaining all the nightmare souls for that stage already, going through the same stage would not garner you any nightmare souls if you defeat those same nightmares all over again. The only way you can make them produce nightmare souls is to re-introduce a new Nightmare Phenomenon into that specific stage. Only then you can defeat the same Nightmares there to obtain their Nightmare souls all over again to add to your soul tally.

Mega Man X6
The Nightmare is a creation of Gate made through the use of Zero's DNA, using it to control the Reploids. Gate employs the Nightmare in a bid to create a Reploid utopia under his rule. Zero Nightmare, a clone of Zero, was made to make the public believe that Zero was spreading the Nightmare. Isoc used this explanation to rally Reploid volunteers to assist his "Investigators" in wiping out the Nightmare, when the actual intention was to gather victims for the Nightmare. However, the plan is thwarted by X and the real Zero; together, they defeat the Nightmares along with Gate.

Zero Nightmare
The Zero Nightmare is a clone of Zero who appears in Mega Man X6{{Infobox Character X| name=Zero Nightmare.

Nightmare Mother
The Nightmare Mother (ナイトメアマザー) is the boss of the first part of Gate's Lab, two giant masses of Nightmare DNA that spin throughout the room, stopping every so often to open their "eyes" to attack. Their only vulnerable area are their mechanical eyes, which are weak to the Metal Anchor or Rakukoujin.

They move around the room in a circular pattern, each one always on opposite sides. (Speed of transition between walls depends on difficulty.) Every once in a while, they will stop to launch their attacks. The attacks include firing blue energy balls from overhead that fly across the screen and strike the floor with thunderbolts, and smaller energy balls that bounce off walls. They can also fire shots similar to the Goo Shaver from Mega Man X5 that travels down walls and across floors. Occasionally, they will stop stacked on the same wall. While the one on top fires small energy balls from above, the other will fire a ball of flame at the floor, causing it to erupt in flames. When one of the two eyes are destroyed, the empty shell of DNA will slam into the walls while the other one launches attacks, further limiting the "room" the player has to maneuver.

The way that they can only be damaged while attacking is very similar to the Devil series of robots (e.g., the Yellow Devil) from the original Mega Man series.

Nightmare Virus
The Nightmare Virus (ナイトメア・ウィルス) is an enemy found in almost every stage (except the intro level and the first Secret Laboratory level). They can attack the player by shooting at them, or by getting close and touching them. If the player is playing on Xtreme difficulty, the virus can also disappear, reappear close to X or Zero, and charge at him. They leave behind Nightmare Souls when destroyed. If the player doesn't take the Nightmare Soul before it vanishes, the Nightmare Virus will regenerate, but only one time and it will not leave a Nightmare Soul when destroyed again.

If it's on the same screen with a Reploid in need of help, it will move in to try and possess them. If the Nightmare Virus is not destroyed or the Reploid is not rescued before the Nightmare Virus gets too close, the Reploid will turn Maverick (which somewhat resembles a zombie version of itself) and attack the player. If a Reploid holding an item is turned Maverick, the item will be lost forever.

Nightmare Bug
Nightmare Bug is a bug enemy that flies near the player. They can only be destroyed by Yammar Option, but this is generally useless as more will always come. They appear in Commander Yammark's, Shield Sheldon's, and Blaze Heatnix's stages.

Nightmare Insect
Nightmare Insect (ナイトメア・インセクト) is a mantis enemy that appears in Commander Yammark's stage. If they are destroyed with any weapon other than the Yammar Option they will regenerate, leaving the player a quick chance to get by.

Nightmare Pressure
Nightmare Pressure (ナイトメア・プレッシャー) is the sub-boss of Metal Shark Player's stage. Presumably, it's the core of the trash compactor that antagonizes the player throughout the whole stage. It can shoot small balls, shoot with pink lasers, and can crush X like a compactor. Its weak point is the pink lasers. The compactor (but not the boss) returns in Gate's stage if the player chooses Zero.

Nightmare Snake
Nightmare Snake (ナイトメア・スネーク) is the name of five red Mechaniloid sub-bosses that appear in Blaze Heatnix's stage. They resemble a mythological creature known as Ouroboros, a snake that bites its own tail and thus makes a circle. They can only be defeated by destroying the four green cores around their frame. They are weak to the weapon gained from Infinity Mijinion, Ray Arrow and Rekkouha, and X's Nova Strike (his Ultimate Armor's Giga Attack). A charged Metal Anchor can take out the sub-boss in one hit, given a bit of positioning and luck. The Giga Attack of the Falcon Armor can take it out in one hit as well. This sub-boss is considered to be one of the most annoying in the whole X series as it appears one after another whenever they are defeated and when the player advances into another portion of the stage. It is also worth noting that on Easy Mode, this sub-boss does not shoot its projectiles from its cores.