at the battle area after the elite 4
Chat with our AI personalities
every weekend he will be at the fight area for a battle
When you go to Stark Mountain you will meet your rival (you won't battle him/her). After that you will be able to face him at the Fight Area on the weekend(Not on Friday).
there is no stark mountain. stark mountain is only in DPP
He returns to the battle zone in the fight area
Go to the fight area duting the weekend or Mount Stark in the week and he will be there to battle with you. he'll have 6 Pokemon so be ready.