: Features the "Nightmare" system and multiple endings.
: Indicates that the original game data was too large for a single file and was split into multiple segments (e.g., part1, part2). You must have all parts in the same folder to successfully extract the contents.
: The series' first (and controversial) transition into 3D gameplay.
: An optional setting that reduces damage taken, making the more difficult titles like X6 more accessible.
: A return to 2.5D graphics with a "Tag Team" character swap mechanic. Key Features
: Known for its high difficulty and the rescue of Reploids.