Magnus Black stands tall with shaggy black hair featuring an ahoge and piercing Persian red eyes. A distinctive royal purple half-mask obscures the left side of his face, leaving only his right eye and mouth visible. His initial attire includes a black tailcoat with grey accents, high collar, and yellow buttons, layered over a black-and-white vest, completed by royal purple gloves. Later developments see him adding a matching cape, wearing black pants with multiple zippers, shorter boots, and a sleeveless shirt.

Born before the Great Collision, Magnus lacks the organic ability to brawl or communicate with Bakugan, initially relying entirely on a specialized gauntlet. He and his younger sister Emily became orphans following a troubled past in a conflict-affected region. Emily suffers from a rare debilitating disease, compelling Magnus to join AAAnimus Inc. in exchange for her promised medical treatment. This bargain drives him to commit morally questionable acts like Bakugan theft and environmental destruction, actions he justifies under a personal interpretation of the samurai bushido code. His masked identity stems from shame over these deeds.

Initially cold and enigmatic, Magnus maintains distance and exhibits quick anger when annoyed. His singular motivation is securing Emily's cure, transforming Bakugan battles from recreation into serious endeavors. He harbors immediate resentment toward Dan Kouzo, perceiving Dan's natural bond with Drago as a reflection of his own inability to connect with Bakugan. This jealousy fuels his rivalry with Dan, whom he views as the primary obstacle to becoming the strongest battler. Despite his alignment with AAAnimus, he demonstrates occasional integrity, honoring promises and protecting innocents during vigilante activities.

His partnership with the Darkus Bakugan Nillious begins as purely transactional, focused on obedience in battle rather than mutual understanding. This dynamic extends to his other Bakugan, Enoch and Fangzor. A significant shift occurs when Nillious voluntarily declares them "partners" during a crisis, challenging Magnus's perspective. Further evolution follows an incident in the Maze that physically rejuvenates him, granting the organic ability to hear Bakugan. This change sparks genuine joy and marks the beginning of his efforts to forge meaningful bonds with his Bakugan.

Possession by the entity Tiko temporarily amplifies his negative traits, rendering him psychotic and arrogant. Defeat by Dan liberates him from this influence, prompting his departure from AAAnimus. Though initially more desperate and power-focused afterward, his interactions with Dan gradually evolve from antagonism toward mutual respect. He eventually accepts Dan's offer for future battles framed as friendly competition. During the final conflict against Tiko, he fights to uphold a promise made to Dan, signaling this changed relationship.

In Bakugan: Legends, Magnus assumes temporary leadership of the Awesome Brawlers after Dan and Athena are accidentally stranded on Vestroia. He coordinates defenses against the extra-dimensional threat known as The Swarm. He masters the Nova Core technique, obtaining Baku-Gear through it. Alongside Dan, he discovers Nova Cores grant diverse abilities like Baku-Fusion, demonstrating his continued prowess as a top-tier brawler.

His relationship with Emily remains central. He initially isolates her to shield her from the dangers of his brawling life, driven by a lifelong vow to protect her. Crystal Blue, a Bakugan encountered on Vestroia, assists him as a translator during his temporary inability to understand Bakugan, though their interaction is marked by frustration over his single-minded focus on finding Dan.