some give me a tip how to train fast and get very high level in creed

The fastest way is to have Toxic on at least 1 Pokemon and Fly on most of the others.
It'd be best if the Pokemon were Golett/Golurk as they have the most immunities to the Mew.

If you can't afford Toxic, the fastest way would be Bird Tamer using a Ghost type and non of Bird Tamer's moves can hit a Ghost type Pokemon.

What icyslash didn't add in is go to you're home town and go to dark alley and fight the dude there with toxic and fly/megahorn - After 1 kill on a mew just restart battle, You don't get anything for completing just xp

to add on top of what ConnerMason said, before you can battle "Mysterious Trainer", you will need to get all 40 gym Badges first.

to add on top of what grim reaper said you will have to by tickets to every region

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If you cant afford toxic you can teach it sludge but its not as good and less chance of it working