Onslaught's introduction into X-Men storylines caused its own crossover event across multiple Marvel comic book titles (including Avengers, Fantastic Four and The Amazing Spider-Man issues).

When Marko declines his offer and decides to warn the X-Men of the danger ahead, Onslaught uses his powers to mentally block Juggernaut from remembering his true identity, and magnetically to fling him from Vancouver to New Jersey.

Additionally, Onslaught had started recruiting others to do his dirty work for him and first manifested himself to the X-Men when he challenged the teleporter Gateway to test Cyclops, Storm, Wolverine, and Iceman, by kidnapping them and sending them to face off against his agent Post.

[7] Onslaught later sought out Jean Grey, hoping to convince her to join his cause with the offer of power rivaling that of the Phoenix Force.

[8] Gradually, Xavier's frustration with his dream of mutant-human harmony began to increase, exacerbated by the daily growth of anti-mutant hysteria, the deaths of dozens of mutants from the lethal Legacy Virus, and his own failed attempt to rehabilitate Sabretooth.

Bishop, remembering childhood stories of a traitor betraying and killing the X-Men, began to realize that the guilty party was Xavier as Onslaught.

Onslaught returned to New York, reprogramming the Sentinel robots to obey his commands and form a protective circle around Manhattan, sealing off the island from the rest of the world.

Their first confrontation with the entity and his minions resulted in the rescue of Xavier, reducing Onslaught to a mass of psionic energy contained within his armor.

During their next assault, Jean Grey used her telepathy to suppress the part of the monstrous Hulk's mind that contained the rationality of his alter ego, Dr. Bruce Banner.

Realizing that Thor's efforts alone were insufficient to destroy their adversary, the non-mutant members of the Avengers and the Fantastic Four entered the energy field.

Onslaught Reborn features the return of the villain and addresses unresolved plot threads;[14] this event is set after the "Decimation" and "Civil War" storylines.

Onslaught swore revenge on the young Franklin Richards and any other hero that he despised, manifesting as a monstrous version of his previous form with a skull-like face.

Back at Avengers Mansion, Rikki Barnes was babysitting Franklin when Loki, Executioner, Scarlet Witch, Enchantress, and Ultron V surprised them with an offer to help defeat Onslaught.

As Rikki races inside the facility to locate Toro, she stumbles into the control room instead, where the sinister voice of her dreams beckons and reveals itself to be Onslaught.

[20] In the lead-up to the AXIS storyline, Magneto is pushed too far by the Red Skull and his S-Men, after discovering that the madman had turned Genosha into a Concentration Camp and was exterminating mutants and inhumans.

The Avengers came to help after locating the Skull following the discovery he was the source of the "World War Hate", who were shortly after joined by the X-Men and other allies.

However, the Red Onslaught deployed two Adamantium Stark Sentinels which had been created by Iron Man under the influence of the Skull's telepathy, with their creation having been wiped from his memories by the villain.

Moira noted on her journal that her actions in manipulating Xavier had broken his psyche and she feared this would eventually unleash something unexpected on the world.

He was able to escape and caused a fight between Fabian Cortez and Lost at Stacy X's orphanage and later possessed every mutant in the Green Lagoon during a meeting between Legion and his father, forcing David and the Xorn brothers to kill everyone there in order to free them from his control.

[30] Onslaught is a psionic entity with superior physical and mental power; possessing the combined abilities of both his progenitors Professor X and Magneto.

At its prime, Onslaught is capable of telepathy, telekinesis, energy projection, sensing mutant presences, manipulating magnetic fields, mind control, flight, mental manipulation, possession, astral projection, perceiving the world around himself as patterns of magnetic and electrical energy, absorbing any mutant into his being and affecting reality itself.

In his first form (when he was one with Xavier), Onslaught showed a wide variety of abilities including immeasurable strength, and incredible resistance and endurance.

Even in his initial form, he also demonstrated sufficient physical strength to punch the Juggernaut unconscious across North America, and to rip the Crimson Gem of Cyttorak out of his body.

While they stopped threats like Ultron and Annihilus, Phoenix also began controlling her allies like Tony Stark, and set her eyes on ways to increase her powers.

While this new version still maintains the aesthetic of the original Onslaught very much present, the main alteration comes in the form of the Phoenix emblem on the entity's torso.

In order to find and kill Onslaught, the Phoenix assembled a team of Wolverines from across the multiverse while sending the original X-Men back to their home.

While Onslaught first presented itself as an amorphous hivemind possessing countless individuals simultaneously, the villain eventually gained enough strength to take physical form - and the result was as awe-inspiring as it was absolutely terrifying.

While the overall aesthetic of the original Onslaught is still very much present, the main alteration comes in the form of Phoenix fire raging from the head and upper torso.

It turns out this was Wolverine's plan all along, and Onslaught grants Jean the power to send each of the team's members to their preferred reality as reward for a job well done.

As with the comics, the battle against Onslaught came at a cost as one of the game’s playable characters, Jin Saotome and Captain America, end up sacrificing themselves to ensure his defeat.