In several of the psot-game guides for Pokemon Sword & Shield, I see that people say that you can rematch the gym trainers in the Wyndom stadium. They say that you need to invite them, but no one seems to describe how to invite them. They are not in their original gyms and they are not in Wyndom stadium.
I feel like it has to be something obvious since no one describes how to do it, but I just can't seem to see it.
Apparently you can also rematch Hop, but again, how?
Best Answer
To be able to invite each gym leaders (also Leon, Hop, Bede, and Marnie), you need to get their gold cards.
You need to have finish the post-game adventure, for next trainers :
Leon : Battle him at Battle Tower
Hop : Finish the post-game by battling him, deep inside Slumbering Weald (You must have begin the post-game part by beginning at this place too, the endgame show that we must return to this place)
Marnie : You need to find her in Budew Drop Inn, then go rebattle her at Spikemuth after the post-game adventure, next to the Pokemon Center
These one are given during the post-game adventure :
Piers : You get it during the post-game
Post-game Gym Leaders : you get their gold cards when you go to their stadium during the post-game
Unknow location :
Opal : I don't remember when or where you get it, probably during post-game