Pass Lewis and pick up a Toxic Orb.  This hold item afflicts the item holding it with the Badly Poisoned status.  There are actually any number of reasons to use this.  Covet or Switcheroo will let you swap it to your opponent’s pokemon, Fling will deal considerable damage and stand a good chance of Badly Poisoning the target, Poison-type pokemon are immune to its effects and might be able to lure an opponent into using Covet, Switcheroo, Thief, or a similar move, and finally on Poison Heal Breloom it makes the pokemon nigh indestructible through escalating passive healing.  Thankfully, the poisoning only starts at the end of the first turn of battle, so you have time to use the moves that go with Toxic Orb before it injures the pokemon holding it.  This makes Toxic Orb a very powerful item, though it’s only very useful some of the time.

Return up the stairs and follow the passage back to the scientist, then return West to the two Ace Trainers.  Head South from there down the passage, and you can pick up a Calcium (the Special Defense vitamin) from the passage by the watery area.  Pass the Ace Trainers going back to the West and return to where you entered the area.

Turn South rather than heading back through the hole in the wall and you’ll run across a gi-clad trainer.

Rotation Battle: Black Belt Corey (1184 Poke)
Opponent: Scraggy Lv 37, Gurdurr Lv 37, Scraggy Lv 37

(Ab)use of Fly will pretty much ruin Corey, whose Gurdurr relies on Dynamicpunch and whose left Scraggy likes Hi Jump Kick entirely too much.

Climb the stairs to the right past Corey and look to the North to find a Nugget.  Go back down the stairs to the main passage here.  Continuing South will let you pick up a hidden Max Repel from a stalagmite, and then you’ll run across a double battle.

Battle: Backpacker Kiyo and Hiker Marcus (2072 Poke)
Opponent (Kiyo): Golbat Lv 37, Swanna Lv 37
Opponent (Marcus): Gurdurr Lv 37, Crustle Lv 37