Magnus first appears in Luminous's storyline. He attacks Guwaru and absorbs a gemstone from him, gaining his powers. Luminous attacks Magnus, but to no avail. The Nova states that he is finished with Maple World and departs, leading us to think of this as some sort of "betrayal" towards Black Mage, as he should have fought against Luminous and prevented him from facing his master, instead. He most likely decided to become a Commander of the Black Mage just to gain even more powers, which he needed to take over Heliseum, but he was never devoted to him. In the present day, Hilla even criticizes him by saying that she doesn't know "why Magnus thought he was smart enough to beguile the Black Mage", and that "his petty intentions were no more opaque than the air itself". She also says that "he could not keep his allegiances straight if they were made of unbendable steel".
Decades ago, Magnus was mentioned to have been exiled from Pantheon for abusing his powers. Magnus assisted Gerand Darmoor, Grandis' Transcendent of Life and the ultimate enemy of the Nova, in taking over Heliseum in exchange for power, disabling its barrier and leading an army of Specters toward it. Kaiser attempted to stop Magnus, but after being outmatched, sacrificed himself to annihilate Magnus' army. According to the spirit of the former Kaiser, the attack would have killed Magnus were it not for Darmoor's power; instead, Magnus was weakened and fled the scene. Meanwhile, Beldar informs Cartalion and Fenelle that Magnus has taken over Heliseum and they discuss that Kaiser will eventually be reborn.
In the present day, Magnus still has reign over Heliseum and resides in the Tyrant's Castle.
In Kaiser's and Angelic Buster's storyline, Magnus sends Nefarious Priests to extract the Relics that powers the barrier surrounding Pantheon. They succeed in removing one of the four while Angelic Buster inadvertently absorbs one of them, causing the barrier to weaken and allow Magnus' Specters to invade. But, with the help of the current reincarnation of Kaiser and Angelic Buster, the Pantheons are able to reclaim the stolen relic, defeat the Specters, and recover the barrier. Magnus himself shows up and defeats Kaiser, Velderoth, and Angelic Buster before retreating. Cartalion mentions that Magnus possesses the former Kaiser's sword, granting him even more power than before. Realizing that they're outmatched, Pantheon's high council decides to send Kaiser and Angelic Buster to the Maple World and seek help from the Alliance.
Magnus makes a cameo in the Dimension Invasion storyline, and is one of the several possible bosses who may participate in leading the assault in the Kritias invasion (if so, the Heliseum mobs are included in the army); however, the players do not confront him directly.
Magnus and his forces invaded the royal family of Heliseum, where he killed Cadena's parents and forced her out of her home. Later, after Cadena got stronger and fought Magnus, Magnus was defeated but fled the scene. Cadena noted that he did not use all of his strength and that his story was not over.
In FriendStory, Magnus's counterpart is the gym coach at Shinsoo International School. In Episode 4 Magnus and Hilla start cracking down on dating in the school which is ruining Hawkeye's "game." Hawkeye proposes that the player tries to get Magnus and Hilla to start dating so that he can go back to "scoring," but to barely any avail as Magnus and Hilla hate each other similar to the MapleStory. Magnus is also one of the judges in the rock off in Episode 6.
If the Hidden Mission of chapter 3 is found and completed, a bonus scene at the end is added where he and Hilla meet, implying that they really are dating - in secret.
- Magnus is Latin for "great." Also, a historical figure named Magnus was a Roman Usurper who tried to overthrow Maximinus Thrax from the throne.
- On hard mode, Magnus's icon glows red.
- The Two-Handed Sword Kaiserion is based on Magnus's sword the Kaiserium.