The top-right Driftveil Market stall is occupied by a man who’s waiting for you to have a level 30 pokemon before he’ll have anything to do with you.  Jerk.  Anyway, if you do show him such a pokemon, he’ll hand you an Expert Belt.  This Hold Item boosts the damage of the holder’s Super Effective attacks an additional 20% on top of the doubling effect they already get for critical hits (triple for those with Sniper).

South of the Driftveil Market is yet another hotel, where you can pick up an Everstone on the top floor to keep a pokemon from evolving when you don’t want it to, and in the lobby is a lady who wants to see a pokemon that knows Embargo.  Show her one and she’ll pass you a Haban berry, a berry that is eaten by a pokemon to reduce the damage of a supereffective Dragon-type attack against it by 50%- not the most terribly useful berry, but then, there are very few reasons to actually use Embargo either.  So it goes.

After all of that, you’re right by the South gate- but don’t bother going through.  The area is reserved for the Pokemon World Tournament, which isn’t ready to start yet.  Instead, head North of town and up the hill, then take a turn to to East.  Here you’ll find the house where Team Plasma N have been living.  The lady you watched Hugh rescue is here, and will bring you to meet Rood, one of Team Plasma’s Sages.  He greets you amiably and offers to tell you about Team Plasma so you can have a better understanding of what’s going on here. First, though, he wants to battle you to see what kind of a trainer you are.

Battle: PKMN Trainer Rood (2700 Poke)
Opponent: Herdier Lv 27, Swoobat Lv 27

With the battle concluded, Rood apologizes for testing you- and then Hugh shows up, complaining that the grunt he was chasing got away.