Mega Man X6

Mega Man X6 plays similar to its predecessor, Mega Man X5. As an action platformer, the game follows the series formula of choosing between eight stages in any order, each culminating in a battle with a boss character whose defeat adds a new unique weapon to X's arsenal, followed by a fixed series of stages that lead to the final boss. Players initially play as series protagonist X, who is skilled at shooting with his X Buster and can now wield the Z-Saber in close-quarters combat. Like in previous games, players can find and equip armors for X that give him additional abilities, beginning the game with his Falcon Armor from Mega Man X5, with the new Shadow Armor and Blade Armor being hidden in pieces throughout the main eight stages. Zero can be unlocked after finding and defeating the boss Zero Nightmare, and he plays with a unique set of abilities, including a more refined Z-Saber fighting style and a double jump.

A unique feature of Mega Man X6 is its "Nightmare Phenomenon" system, which, after leaving a stage for any reason, causes additional effects or obstacles called "Nightmare Effects" to be added to other stages, such as small invincible enemies or gusts of wind. Stages that have a new active Nightmare Effect are highlighted in red on the stage selection screen. Every stage has a predetermined group of Nightmare Effects that can be added to them, and only the most recent Nightmare Effect for a stage will be active at a time.

In the 22nd century, humans live alongside human-like robots called "Reploids". Following the Eurasia space colony incident, which nearly destroyed planet Earth, the Maverick Hunter Zero remains missing in action and presumed dead, with his partner X remaining as the world's best Maverick Hunter. As a result of the space colony's impact, Earth's surface has been rendered largely uninhabitable, forcing the human population to take refuge underground. An intelligent Reploid researcher named Gate, researching the impact site, discovers an unusual piece of wreckage. A week later, Gate loses his sanity as he secretly experiments on the mysterious item and declares his intention to turn Earth into a utopia for high-class Reploids.

Maverick Hunter operator Alia sends X to the crash site to investigate the disturbance. During his mission, he briefly encounters a ghostly being reminiscent of Zero. X then meets a Reploid scientist named Isoc and his nigh-invulnerable subordinate, High Max. They are in search of the Zero-like being, dubbed the Zero Nightmare, which is spreading a dangerous "Nightmare Virus" that causes Reploids to falsely perceive reality to the point of harming themselves and others, turning them into rebellious "Mavericks".

Series producer Keiji Inafune was not involved in the development of Mega Man X6. He had originally intended for the fifth chapter in the series to be the last due to the death of Zero at that game's conclusion. "And so I'd always planned to make Zero come back to life in the Mega Man Zero series, but then X6 comes out sooner from another division and Zero comes back to life in that, and I'm like, 'What's this!? Now my story for Zero doesn't make sense!

Zero's been brought back to life two times!'" Inafune also felt he owed fans of the series an apology for the decision to create Mega Man X6, although the series was "starting to go in a direction out of [his] control" at that point.

According to the Japanese magazine Famitsu, Mega Man X6 was the seventh-best-selling game in Japan during its week of release, with 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 received mixed reviews, with an average score of 65 on Metacritic. It has often been criticized for its harsh difficulty, stemming from poor design of its stages and mechanics, as well as its recycled narrative. Giancarlo Varanini of GameSpot was disappointed by the execution of the Nightmare System and item collection, which added variety and longevity but were not important to completing the game. He praised the game's music, but commented that the visuals were not at the standard set by older games in the series.