Meanwhile, X is awakened by Alia after a dream involving Zero, and she informs him of a large Maverick near Eurasia. He briefly encounters a being reminiscent to Zero, although the being appears distorted and discolored. X then meets a scientist named Isoc and his subordinate, High Max, who are in the search of the Zero-like being, which they identify as the "Zero Nightmare". Isoc invites all Reploids to join his cause to destroy the Nightmare phenomena, which is turning the Reploid population into Mavericks. However, this is revealed to be a ruse to lure Reploids to areas affected by the Nightmare, where they will become Mavericks under Gate's control.
X journeys to the suspected areas to investigate the Nightmare phenomena and rescue the Reploids who volunteered to help. He learns that Isoc's eight investigators have been infected by the Nightmare and become Mavericks. During his battles, X can also encounter the Zero Nightmare and defeat him. Following this, the real Zero appears, unaware of how he survived his battle against Sigma.
Following the defeat of the eight investigators (or High Max), X meets Gate, who reveals he found a piece of Zero's DNA at the Eurasia crash site. The DNA drove Gate insane, and he created the Nightmare phenomena alongside the Zero Nightmare to help build his utopia.
The Hunters go to Gate's laboratory to put to a stop to his plans. Following Gate's defeat, he confesses he has rebuilt Sigma, but Sigma is a shell of his former self: a partially coherent, half-built body, with his programming still severely damaged. However, Sigma has enough strength to nearly kill Gate, and challenges X and Zero. With his sanity slipping, Sigma is once again defeated and one of three endings will occur, depending on which character defeats Sigma:
If X defeats Sigma and previously defeated the Zero Nightmare, Zero is alongside X as he rescues Gate so that Alia, his former colleague, can try and revive him if she chooses to do so. The three make a pact to repair the devastated Earth, while Gate's ultimate fate is never revealed.
If X defeats Sigma, but did not defeat the Zero Nightmare, Alia is instead with X at the end, who thanks him for rescuing Gate. X leaves Gate's fate up to Alia, which is left unknown. Zero is then shown to be alive, but refrains from revealing himself to X and Alia, despite the two being able to sense his presence. Zero says he'll be leaving the fighting to X for a while, as there's something he needs to do.
If Zero defeats Sigma, he is seen at a laboratory at an undetermined period in the future. Fearing that he still possesses the Sigma Virus and could become a Maverick, he requests to be placed in stasis. An unknown scientist agrees to help him, and seals Zero away for the next 102 years, presumably leading to the events of the Mega Man Zero series.
Gameplay
The gameplay is very similar to Mega Man X5. The player can select X with the option to outfit him with different armors offering unique abilities (most of which have to be downloaded, as always, through Dr. Light's hidden capsules.) Zero can be unlocked after finding and defeating the Zero Nightmare, bringing his own weapons and techniques to the fold, including a refined Z-Saber fighting style. Both characters can be equipped with various power-up items earned after rescuing certain Reploids.
Mega Man X6 has an increased emphasis on rescuing Reploids over previous titles in the series. Whereas previous games rewarded the player with health or an extra life, Mega Man X6 rewards the player with additional parts or other permanent prizes. Rescuing Reploids was made more difficult in this game with the addition of the Nightmare, which makes any Reploid it infects evil, thus rendering the Reploid impossible to save. The parts system was altered as well. Rather than attach a certain part to a certain armor, parts are attached to the character itself. The number of parts that can be equipped at once is dependent on the player's rank, which is increased by harvesting Nightmare Souls.
Depending on the player's actions during the game, it's possible to unlock what are normally the final set of stages, namely Gate's laboratory, much earlier than normal than what is considered the norm for the X series; with the exception of Mega Man X5, players normally had to defeat the 8 main bosses before unlocking the final stages. In X6, defeating both the Zero Nightmare and High Max, Isoc's bodyguard, are enough to unlock Gate's laboratory before even defeating most of the main bosses.
Reception
According to the Japanese magazine Famitsu, Mega Man X6 was the seventh best-selling game in Japan during its week of release at 39,318 units sold. Dengeki Online reported that Mega Man X6 sold a total of 106,980 units in Japan by the end of 2001, marking it as the 109th best-selling game of the year in the region. The game eventually saw a re-release as part of the PlayStation the Best range of budget titles. Mega Man X6 was also included on the North American Mega Man X Collection for the Nintendo GameCube and PlayStation 2 in 2006.
Mega Man X6 received mixed to positive reviews, with an average score of 69% on GameRankings. GameSpot gave the game a 7 out of 10, saying that the game is "a disappointing effort. The nightmare system and item collecting add variety and longevity to the game, but... The graphics aren't really even up to the standards set by older games in the series, and while the music is good, there aren't any tracks that particularly stand out. Despite these shortcomings, it's still Mega Man, and the gameplay is still entertaining, making X6 an attractive package for hard-core Mega Man fans." IGN gave a more positive review, an 8 out 10, stating "It's an all-new Mega Man game, yet it's still pretty much the same. There's nothing wrong with that"; they praised the soundtrack and replay value. Among the most negative reviews, Electronic Gaming Monthly gave the game a 3.5 out of 10, saying "I thought I’d sooner see Sasquatch ride a Chimera bareback through the streets than a bland series like Mega Man X last through six installments."
In retrospective, 1UP.com referred to Mega Man X6 as "sloppy" citing multiple issues within its design such as repetitive stages and background images.
