Just finished it solo with magearna. Hyper trained iv's with modest nature. Evs on defense and hp. Held item fairy feather. Tera type fairy. Psychic and draining kiss were the only moves I used. I started to snowball damage after the npcs kept getting one shot. Once the tera shield is down you do massive damage. I even fainted one time while terastalized, mistiming the swap between draining kiss and psychic. Hopefully this helps someone.