The assassin droid IG-72 captured two MagnaGuards on behalf of the scientist Treun Lorn, to be used as part of Nycolai Kinesworthy's research with the remains of General Grievous. The result was N-K Necrosis, a killing machine in the vein of Grievous himself. The NK-3s were used to train the Necrosis droid in the lightsaber forms Grievous had once instructed his guards.
The NK-3s and Necrosis itself were ultimately defeated by a rag-tag band of spacers in the Myyydril Caverns on Kashyyyk. The droids' remains were stripped of all valuable possessions.
NK-3's appeared in the video game Star Wars Galaxies, a massively multiplayer online role-playing game developed by Sony Online Entertainment and published by LucasArts, prior to its closure on December 15, 2011.