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.[2][3] 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.[4][5]
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.[6]
Mega Man X6 has an increased emphasis on rescuing Reploids over previous titles in the series. Whereas previous games rewarded players for rescues with health or an extra life, Mega Man X6 rewards players with additional parts or other permanent upgrades.[7] Rescuing Reploids was made more difficult in this game with the addition of the Nightmare Virus, an enemy that turns peaceful Reploids into dangerous "Mavericks" when it touches them, thus rendering the Reploid impossible to save. Certain Reploids grant power-up items called "parts", a feature returning from Mega Man X5.[8] Rather than parts being equipped to X's armor, parts are now attached to the characters themselves. The number of parts that can be equipped at once is dependent on the player's rank, which is increased by collecting "Nightmare Souls", small items that drop from defeated Nightmare Virus enemies.[9]