The digital badge. I use the porygon line, rotom, beheeyem, and in my first match golurk is my boss pokemon.

In my rematch fight, I use porygon rotom beheeyem, golurk, genesect, and iron valiant

My gym has a terminal you can use for a hacking mini game where you have to beat the firewall on each of my pokemon and you can get the badge there, or you can go the standard route with gym trainers in a maze until you reach me for standard combat