That guy is 10 levels above your party, has stats better than mega rayquaza, and all of its stats are raised by one stage when the fight begins. Since I didn't want to grind up by team 10 levels, I fed my Malamar rainbow beans so it could live on 1 health, then used Topsy Turvy to make its stats shite, and wore it down with fake out and fast Pokemon. I would've glared it, but its psychic attacks were too strong for my Arbok.

Before I fed my Malamar rainbow beans, it shredded all of my Pokemon in one shot.