how to win against Magnus

The best way to beat Magnus is by playing better.

The easiest way to win against Magnus is to play a game other than chess against him. I suggest scrabble or cribbage.

either cheat
or
pray that his internet breaks in the middle of the game

Stockfish. You've got all this power at your fingertips. Magnus won't know what hit him.

Easiest way to beat Magnus is play better as you can and make best moves in the game..

or just play against 6-year-old him

Simple:
Switch the knight and bishop while he's in the bathroom and hope that he doesn't notice:

I've seen a video of magnus going furious when he lost.

@clousems Magnus's IQ is 190, I bet you won't beat him in other games either.

I wouldn't be so sure: I'm fairly good at cribbage and scrabble, and I would bet money I could beat him in Egyptian Ratscrew. Not to brag, but I'm really, really good at Egyptian Ratscrew. Same goes for Bananagrams.
I also doubt that Magnus has the killer instinct necessary to best me in Candyland.