This is the Multiverse Trope actually done right
What's the Work?
Arcane is an amazingly animated Netflix series based directly on the League of Legends video game series, it focuses on the conflict between twin cities Piltover and Zaun and how two sisters end up on opposing sides after tragically losing their family in a rescue attempt.
Who Is He?
The Mage ultimately revealed as an alternate Viktor is a minor yet pivotal character in the show. He is an alternate Viktor who succeded in his plan to bring forth the Glorious Evolution and caused the destruction of all life in Runeterra, left alone amid the wastelands to reflect and realizing the error of his ways, he would go back in time to kickstart the series by giving Jayce the gemstone as a child, trying every possible combination until a good ending was achieved.
What Has He Done?
The Mage being an alternate Viktor presumably shares all his admirable deeds from Season One and early Season Two before his eventual fall to villainy, however unlike the main Viktor, this one would succeed in his plan which would ultimately destroy all life and leave the world a barren wasteland devoid of any humanity. In the years since his victory, Viktor would realize his wrongdoings and choose to amend by aiding an alternate Jayce in stopping him and preventing this dark future from ever coming to be. Arriving at a point in time where a young Jayce and his mother were freezing to death in a blizzard, he used his magic to transport them into a clear plain, saving both their lives and granting the young Jayce a rune before departing. This incident would become Jayce's main inspiration and drive him into his research of magic and the Arcane, all of which led to the creation of HexTech.
Years later, when Jayce, Ekko, and Heimendinger were inspecting the anomaly, the Mage would once more intervene by bringing Jayce to the far future into his world to show him the massacre that Viktor and Ambessa would cause and get him to realize that he needed to destroy HexTech. All the while he would silently watch him from afar, with the intention of getting Jayce to reach the top of what was once Piltover and find his own corpse to meet him there. After meeting with Jayce, he revealed his true identity and intentions, and with Jayce now motivated and determined, he sent him back to the main universe armed with the knowledge to defeat his past self and prevent the Glorious Evolution. The Mage's actions are what gave Jayce the memories of the future that Viktor accesed and made him realize what his actions would lead to, causing his redemption and subsequent sacrifice.
Admirable Standard
The Mage is the sole reason why the entire world of Runeterra was saved from suffering the same fate as his world, in being devoid of all life as a barren wasteland with destruction and mindless Evolved, since he was the one who brought Jayce to the future to see the consequences and provided him with the Rune that motivated him and made the entire series possible as well as sending him back and allowing him to go against Viktor and unite Piltover and Zaun in a war against Ambessa and Viktor's Evolved.
Inconsistencies
Well, much like the original Viktor, The Mage did fall to villainy and became obsessed with achieving the Glorious Evolution, only that this time he actually succeded and caused the death and forceful evolution of every known being in his timeline, effectively committing omnicide by stripping the humanity away from everyone in his world and forcing them into a FWTD by leaving them as mindless evolved to wander the remains of their world. Also, we are shown in extent how horrible this outcome is, with Jayce experiencing it firsthand seeing the remains of all that he's known and almost going insane due to what he's seen. Even if he grew remorseful, changed for the better, and returned to good, his actions are still to heinous for him to qualify as NPG
Final Verdict
Yeah