Killer Sphere (キラースフィア) is a sphere Mechaniloid that appears in Dark Necrobat's stage and the final Sigma stage. It cannot shoot and only attacks by rolling towards or falling on top of X or Zero. It can be easily destroyed by the character's native weapon (the X-Buster or the Z-Saber). It's also weak against Fire-based Weapons as well (Ground Fire for X and Quake Blazer for Zero).