A clone of the original Mephisto, Zwei was the latest Dark Giant created by the master of the Space Beasts and Dark Giants. He was created in response to the fact that the original Mephisto's host Mizorogi Shinya was free of the dark lord's power meaning the mind of Mephisto was dead. The dark one set events in motion first by returning Mizorogi's memories, in a similarly horrible fashion as the method the former dark Deunamist used on other people. His memories and skills restored, Shinya broke out of Fortress Freedom taking Mizuo of the M.P as hostage. As Hiroyuki Misawa was pursuing Mizorogi as he was escaping Night Raiders' base the Memory Police agent was met by Unknown Hand .
While initially recognizing another member of TLT, the dark one showed his true colors to the boy and made him his slave. As Shinya was cornered, he surrendered to Komon and Nagi only to be shot through the shoulder by Hiroyuki. Hiroyuki showed himself to have been taken over by the darkness and turned into Dark Mephisto ZweiMephisto Zwei defeated Mephisto
. Ultraman Nexus came to the scene and the two began their battle first on the ground and then the air. Mephisto Zwei proved too strong for the hero to handle and fast enough to keep up with the third Deunamist. Ren was kick into a cliff and pinned down as Zwei attempted to drain him dry of his energy. As Mephisto Zwei started to absorb Nexus's energy Shinya morphed into Dark Mephisto and saved Nexus. Mephisto appeared to have the upper hand as he fought Mephisto Zwei until he was impaled with the impostor's version of the Mephisto Claw. As his dying action Mephisto held Mephisto Zwei in place for Nexus to use the Arrow-Ray Storm to reduce the impostor to blue particles. While Hiroyuki was freed from Mephisto Zwei the conflict revealed that he and Mephisto were both puppets of the Unknown Hand despite Mephisto's use of agents and his diabolical plans.
Dark Mephisto Zwei as his name implies, is a clone of the original Dark Mephisto. In theory he has all the same powers, abilities and attacks as the original Mephisto but only demonstrated the following attacks:
Dark Ray Storm: Same as the original but was never used.
Speed:Unlike his template, Zwei has greater speed and agility to keep up with Nexus' Junis Blue mode.
Dark Phalanx: Zwei can use his speed combined with Mephisto Claw's attack to attack enemy in a fury.
Strength: Unlike his template, his is much stronger than before.
Dark Ray Feather: Zwei can fire arc shaped bursts of energy, just like his template. However, Zwei can fire it in three consecutive bursts.
Dark Burst Cluster: Zwei uses the same Dark Ray Cluster attack as his predecessor. Unlike his template, it have a certain degree of induction.
Dark Flame: Zwei can fire a light bullet from his right hand. Can be fire in consecutive.
Mephisto Claw: Zwei also uses the claw form from the modified Armed Nexus on his right arm.
Energy Drain: Zwei can absorb the energy of other beings. Something the original never exhibited.
Hiroyuki Misawa (三沢広之Misawa Hiroyuki?)/Dark Mephisto Zwei (ダークメフィストツヴァイDāku Mefisuto Tsuvai?): He was part of the Memory Police that fell under control of the Unknown Hand. He has the same powers as Dark Mephisto and only differs in eye color with Zwei being red instead of black. Thanks to the interference of the original Dark Mephisto, now on the side of good, Zwei is destroyed by Nexus. It is unknown what happen to Misawa after defeated by Nexus. However, he could be reverted to human form or die like his template.