The protagonist, Lin Xuan, is transported to the Marvel Cinematic Universe (MCU). From the start, he gets an outrageously powerful account-stealing System that lets him ignore the rules of the world and log in directly as powerful characters from the Myriad Worlds.
While the Avengers are struggling to deal with the Chitauri during the Battle of New York, Lin Xuan logs in as Saitama, the One-Punch Man, and punches the space portal and the alien mothership behind it into cosmic dust.
When Thanos arrives on Earth with his fleet, Lin Xuan counters by logging in as the Emperor Armor. With a single move, “Emperor’s Demon-Slaying Annihilation Slash,” he cleaves the Sanctuary II and its fleet to pieces.
Magneto wants to control metal? Lin Xuan logs in as the RX-0 Unicorn Gundam. Bathed in the brilliance of its psychoframe, Magneto discovers that the magnetic control he has always been so proud of is a joke.
Dormammu wants to devour Earth? Right in front of Doctor Strange, Lin Xuan logs in as Kamen Rider Ohma Zi-O and points at Dormammu. “I am the supreme and benevolent Demon King, master of time. You, get out of my timeline!”
From then on, the Marvel Universe goes completely off the rails.
S.H.I.E.L.D. lists Lin Xuan as a top-level “Beyonder” threat. The Avengers try to recruit him, only to discover they can’t keep up with his version updates.
The Celestials descend to judge Earth? Today Lin Xuan logs in as Exodia, tomorrow he pilots EVA Unit-01, and the day after he becomes the Lightan. He beats the Celestials so badly they start questioning reality.
Throughout the Marvel Universe, tales spread of a mysterious being. No one knows who he really is. They only know that he can become whoever he wants to be.
It doesn't look good if it's direct
The Marvel timeline is wrong, the Mind Scepter was given by Thanos
Chapter 14: Persuading to retreat, I don't know what to say