A telecommunicator is located in the entrance of the Agate Arena.
<Player>! How is our favorite champion doing?
So you've reached Hardy, yes? You're nearly there! Okay, so the first thing you need to know is that like me, Hardy fights in Doubles. His main strategy is something like a brute force attempt-- outspeed and punish both opponents at once. His signature move Rock Slide is great at that, on top of a notable Flinch chance.
When fighting in a Rocky Field, flinches can be especially nasty, as being knocked into a rock will add additional chip damage. For that reason, contrary to what you might expect from a Rock-type Leader, Speed will be critical in this battle. If you don't move fast, you might not move at all, so Pokémon with strong priority moves may be at a particular advantage here. Further, Hardy's Pokémon may use the stomes as defensive cover from some attacks, so be careful how you approach. The field provides him little resistances otherwise though, so if you can find an opening, take it! Whatever the case, I'm sure you'll figure out something. You always do, right, Champion?