The carbon knife is a melee weapon that Deimos uses in Madness Combat 5.5, Madness Combat 6.5 and Madness Combat 9: Aggregation. Sanford also uses it to kill several A.T.P. soldats in Madness Combat 7.5. It first appears in Madness Combat 8: Inundation, where it is in the hands of A.T.P. engineers throughout the animation. The carbon knife also appears in Madness: Project Nexus along with a version with a longer blade called the carbon sword.