Nihilist!Tagg, also known simply as The Nihilist is one of Tagg's aspects, and the most dangerous and evil of all. A manifestation of Tagg's inner pain, he was normally kept at bay by the numerous other aspects inhabiting Tagg's mindscape.
Taking this opportunity to be free, Nihilist!Tagg hijacked Tagg's body in short order on October 15th, and then mind-controlled Muddy, Doc, Crochet, Thresher, Sentinel, Limna, Draca, Hydreigon, and Helios, as well as Cobalt offscreen. Victini, being a legendary, was able to resist Nihilist!Tagg's control, leading him to seal him inside his GS Ball. Xatu managed to resist just long enough to teleport them away from the hotel, preventing Nihilist!Tagg from going on a murder spree immediately.
Luke, Tracer, and DS along with their mons confronted him there, after he had Doc, Sentinel, and Xatu use Telekinesis to bash the three trainers against trees and each other. The battle was a hard fought one, with Nihilist!Tagg using his mind-controlled mons to put Vlad, Lardna, Iggy, and Teala in the ICU, as well as Xatu teleporting in Coulomb to fight at one point, the Eelektross mauling and burning Guardé and Chord into the ICU as well. Eventually, Diesel was able to put Tagg to sleep and Swindle returned Cynical!Tagg, allowing the combined aspects to defeat Nihilist!Tagg and place him behind a stronger seal.
Following the reveal of Crewe's true species, the empathetic backlash from everyone managed to weaken Nihilist!Tagg's seal. While the J-Team was attempting to find their way through the various mindscapes, Noir managed to escape Fool's mindscape and made a deal with Nihilist!Tagg, the aspect powering him up into Nihilist Soul.
Upon meeting the J-Team once again, he gloated about what he did the first time, before attacking them alongside Noir. Summoning Tagg's immense pop culture knowledge, he transformed first into Dark Hide and then No Heart. In his final form, he froze time to critically damage the trainers, but was thwarted by the combined efforts of Silver!Tagg and the giant Archen from Tracer's mindscape, Pentigan using a Black Soul Gem to seal him within.
Nihilist!Tagg made a brief appearance inside his Soul Gem, lamenting the fact that Noir was going with one of Pentigan's aspects.
Personality and Abilities
Being a manifestation of Tagg's inner pain, Nihilist!Tagg would like nothing more than to see the world burn. He was also extremely sadistic, taking great pleasure in the pain he caused to Tagg's friends, even laughing about it before the second battle.
In terms of fighting ability, Nihilist!Tagg exhibited Auric techniques that Tagg was unable to use until long afterwards, such as his Aura staff. His most dangerous skill was the ability to mind-control other beings by mixing his Aura with their own via the threads made perceptible via Aura Sense. As a side effect, it also made Tagg's weaker teammates far stronger, allowing them to trade blows with their far more experienced opponents.