So, this is the main department store of the Unova region and where you can go for a wide variety of items! Additionally, there are a couple of trainers looking to battle (battles in a department store, how bogan!). Let's get exploring! To the west of the front counter on the lowest floor is a Lady in white dress.
Apparently she's clueless when it comes to shopping and wants you to buy a Hyper Potion for her; she'll also pay you $1200 to buy it. Once you have a Hyper Potion--from the mall or your own pocket--speak to her again to receive an Energy Root for your efforts.
To her north, standing in front of the western set of stairs is the first trainer battle here. Moving into her line-of-sight doesn't trigger a battle, luckily, only if you talk to her. When you do, the battle will start!
Trainer Battle: Waitress
Head to the east side of the bottom area and you'll see a door on the back wall head through. Inside you'll find an storage area with an item in the north-east corner. Grab it to find that it's a Poke Doll . Once you have it, head back out.
Note : If you have Rotom in your party, you can change its form at any time by inspecting the storage boxes.
From there, head up the main, central set of stairs to the very top floor. There's a Waiter here. Same thing as before, if you speak with him, a battle will begin.
Trainer Battle: Waiter
Besides the shops themselves, there's not actually anything else to do here. Below we list all the shops by location. Note that there are Vending Machines on the eastern side of the top floor.
Bottom Floor Western Clerk
Potion, Super Potion, Hyper Potion, Max Potion, Revive, Antidote, Parlyz Heal, Burn Heal, Ice Heal, Awakening, Full Heal
Escape Rope, Poke Toy, Repel, Super Repel, Max Repel
Middle Floor Western Clerk
Poke Ball, Great Ball, Ultra Ball, Heal Ball, Net Ball, Nest Ball, Dusk Ball, Quick Ball, Timer Ball
Greet Mail, Favored Mail, RSVP Mail, Thanks Mail, Inquiry Mail, Like Mail, Reply Mail
Middle Floor Eastern Clerk
TM15 - HyperBeam, TM68 - Giga Impact
Top Floor Left Clerk
Protein, Iron, Calcium, Zinc, Carbos, HP Up
Top Floor Right Clerk
X Speed, X Attack, X Defend, Gaurd Spec., Dire Hit, X Accuracy, X Special, X Sp. Def
Once you're done here, feel free to head back to Route 9.