I believe someone is cheating by speeding up a clip. How do you report them?

( In all levels I was faster than him but overall I was 1 second slower. Not possible)

You should probably message a moderator with the appropriate information, and they will deal with it.

Hey Re69, you can pm me the run you're talking about and I'll look into it

It could be the case that their transition time between levels is faster. I.e. they press next level faster