I don't play OU but whatever.
Stunfisk-Galar @ Leftovers / Air Balloon
EVs: 252 HP / 4 Atk / 252 Def
- Stealth Rock
- Thunder Wave
I think this is an ok moveset. It sets up rocks. It uses Yawn, which makes people want to switch out, and get hurt by rocks. I guess you could give it Protect to compliment Yawn, but IDK. Thunder Wave just cripples things. I gave it Earthquake since that is a strong move. I made it defensive but it could also be mixed, or specially defensive.