Time travel

"... and that's it," said Thanos.

Then Alex replied,

"So to keep it short, I single-handedly defeated your army and you, but then an unknown third party showed up and gave you powers that defeated me."

"Yes," answered Thanos.

So Alex then knew that if this world got attacked, that could mean something happened to the god who sent him here.

'Great.' He thought sarcastically.

"Thanos, you know you've gone a little too far with your plan. You've even lost control of this world." said Alex.

Thanos then sighed and said,

"How did you know?"

"It's pretty easy to guess, you know?" answered Alex.

Alex then thought, 'To make sure that the being who gave power to Thanos is not from this world, I'll have to come back to the past marvel.'

After a few seconds of thinking, Thanos said,

"Do you plan to return to when you were born?"

"How did you know?" answered Alex.

"Just taking a guess."

Then Alex thought, 'Should I bring my friend? No, it would bring unwanted attention from destiny changing if it wasn't already broken. '

"Goodbye, I guess," said Alex as he waved at Thanos.

Alex then charged lots of energy that far surpasses everything that exists in Marvel, and that surpassed even Eternity, which is the manifestation of the multiverse in which Marvel resides. (1)

Thanos and nearly all of the beings that lived in Marvel passed out. The only beings that could avoid passing out were the manifestations of each different universe and eternity, but even they were scared by this power.

Has the energy was released in a way to rewind everything in the multiverse back to where it started when he was two years old. Even if this cost lots of energy, it was nothing for the current him because it only drained a tenth of his energy.

As everything turned white, he thought, 'I need to do a complete reset of everything and I'm quite lucky to know everything about the celestials and the manifestations of the universes and the manifestation of the multiverse in marvel.'

Then everything seemed to come back to where they were in time, but then everything started to slowly go back. It was accelerating until everything stopped in front of a two-year-old baby.