???

??? is the subconscious manifestation of Mob's Boundless psychic power that was consciously repressed in order to appear normal. ??? was formed as a result of Mob bottling up his emotions and refraining from using his psychic powers due to "that" incident in Mob and Ritsu's youth.

Appearance
As a subconscious entity, ??? does not have a true form or appearance though its presence in the outside world can be perceived by Mob's eyes glowing completely white, his hair flaring wildly, his body becomes shrouded in darkness and a dark-coloured overwhelming aura encompassing him. In the anime, this version remains the same with the addition of sketchy and messy lines in place of the regular animation. In Mogami's mind, its appearance looks less human, appearing as a messy black shape with a smoky aura and scribbled in white marks for eyes. The change in appearance is likely due to Mob's mental body being destroyed and the only being thing left is his powers.

When viewed inside Mob's mindscape, ??? appears to be a completely featureless version of Shigeo.

Personality
As the subconscious manifestation of Mob's repressed psychic power, it views itself as Mob's truest existence, something which has been alluded to by other characters.

It only ever manifests itself in the physical world when Mob loses consciousness in a situation of extreme stress or when Shigeo's physical body is destroyed, as seen during his fight with Mogami, whereupon it proceeds to either destroy the cause of the problem or carry out Mob's current desire. It explains that it does this for its own sake as it can do what it wants to do. It lives to be itself, and does not like Mob because he views him as the person who has kept him locked away by never truly embracing his psychic powers and only using them on the rarest of occasions. Despite having the same general desires as Mob, such as his attraction to Tsubomi and love for his brother, it does not trust anyone else or any of the people that Mob interacted with and made friendships with throughout his time in middle school.

History
One day, when Ritsu and Shigeo were younger and were walking home, they were surrounded by three adolescent thugs. These bullies took their New Year's money, and when Ritsu tried to get it back, they began beating him up. Shigeo tried to stop him, but he was effortlessly overpowered by one of the other bullies. In that moment, Shigeo's desire to protect his brother and the extreme emotional stress caused ??? to awaken for the first time. It then defeated all three bullies, sending them crashing to the walls and causing them to bleed, and it inadvertently injured Ritsu as well. This experience left Ritsu traumatized, and it is what led him to develop an inferiority complex and jealousy toward his older brother for his psychic powers.

Teruki Hanazawa Arc
??? first appeared after Mob was knocked out from Teruki Hanazawa strangling him. ??? proceeded to massively overwhelm Teruki, before destructively lifting up the destroyed school building's debris high into the sky.

Keiji Mogami Arc
??? next appeared while Mob was inside of Keiji Mogami's mental world after Mob's mental body was destroyed by Mogami's rampant spirits. After manifesting, ??? immediately absorbed all of the spirits and released its colossal psychic power in destructive waves, destroying Mogami's mental world, freeing both Mob and Minori Asagiri from his possession.

???% Arc
??? then surfaced after Mob was knocked out after being hit by a car on his way to meet Tsubomi. Awakening because it had predicted it would be needed for such an important moment, ??? destructively continued on the journey to meet with Tsubomi, laying waste to the city and anyone who got in its way. After encountering Ritsu, Mob was finally able to confront ??? head on, where ??? explained its desires and motivations for the way it acted as well as revealing it would take control of Mob. Mob then explained why what it was doing was wrong and told it that he would come to accept ??? as a part of himself. At that, despite fearing rejection from Tsubomi, ??? eventually accepted and assimilated with Mob, signifying Mob's acceptance of psychic power, and more importantly his willingness to love himself.

Powers & Abilities
As ??? is the subconscious manifestation of Mob's repressed psychic power, it represents the full and unrestrained extent of Mob's psychic power. As such, it is capable of all the feats Mob is capable of, though on a much greater and far more destructive scale. For example, ??? has a much greater ability in absorbing psychic energy, being able to absorb the energy from other espers and the atmosphere around him without the need of getting into close proximity to the source.

'''Energy Absorption: ??? '''can absorb the energy from other espers with ease where Mob himself would struggle. While Mob himself was shown to have difficulty absorbing Serizawa's power and nearly die trying to do the same for Toichiro Suzuki. In ???'s case, it was able to easily absorb energy from Teruki Hanazawa on two occasions and even Suzuki. It appears to do so subconsciously and without effort.

Matter Absorption: During its battle with Teruki Hanazawa, ??? absorbed energy from the atmosphere and converted rubble into energy for its use.

Technokinesis: It appears that ??? has the ability to influence or stop electronics, similar to Hatori, as Joseph noted that electric devices in the surrounding area had stopped functioning, such as cars and helicopters.

Mass Exorcism: During Mob's fight with Keiji Mogami, 100% Courage Mob, his most powerful form outside of ???% itself, was briefly able to match the power of Mogami and his spirits. However, he ultimately lost. When ??? surfaced to save Mob from death, his presence instantaneously erased every spirit under Mogami's control and the dimension itself where they fought. Mogami himself, however, managed to escape.

Massive Disasters: In the final arc of Mob Psycho 100, ??? traveled across various cities to find Tsubomi and proclaim Mob's love for her. Simply by walking toward her, ??? destroyed nearly everything in its path. The various disasters it left in its wake became increasingly devastating from simply destroying the ground, nearby trees, and fences to obliterating skyscrapers as well as causing earthquakes and tornadoes plus ??? is omnipotence

???'s feats include effortlessly defeating Teruki Hanazawa and destroying Black Vinegar Middle school before raising all the debris high into the sky, entirely destroying Keiji Mogami's mental world (thus freeing himself from it and Minori Asagiri from Mogami's possession), creating tremors and strong winds powerful enough to span several cities and laying waste to a large area of Seasoning City on the way to meet Tsubomi (effortlessly defeating Teruki Hanazawa and Toichiro Suzuki in the process). It is undoubtedly true that in this state, Shigeo is the strongest esper in the entire series.

Quotes

 * "I knew I would be needed."
 * "I am me. I am Shigeo Kageyama."
 * "Ahh...so you're "Mob." The fake me."
 * "No one can stop me."
 * "Why am I doing this? For my own sake. To do what I want to do."
 * "If you crumble into nothing like this...I won't have to hold back anymore. I'll get to anything."
 * "No one will save me."
 * "It is because I am in this state that I need to let Tsubomi-chan see me. If she were to accept me like this, that would be...bliss."
 * "I am not a tool. I cannot be tamed by another person."
 * "I want you to accept me as well."

Notes & Trivia

 * ??? is implied to have first manifested during an incident where he passed out and awoke to find knocked out bullies and an injured Ritsu. It is this event, and the witnessing of ???, that traumatized Ritsu and caused him to fear and be jealous of his older brother's psychic power.
 * Despite being born from and a part of Mob, it seemingly exists separately within Mob as destroying the vessel that contains it, such as when Mob's body was destroyed by Keiji Mogami, unleashes it.
 * In the MP100 X Hito Kui crossover, it was shown to be possible for ??? to manifest physically while Mob is 'conscious' or while Mob is trapped in a place where he cannot use his psychic powers, as both were the case while Mob was in dream-world of the "Devourer", implying that ???% is not a part of Mob's regular psychic abilities. XXXX (presumably the "Devourer" himself) commented that "[Mob] is no regular person".
 * It's possible that ??? is released when Mob is about to die as a type of survival mechanism.