During battle, Pokémon can be stuck with a variety of different afflictions, damaging them or hindering their ability to attack. There are plenty of options to cure these conditions, but one of the handiest is the Lava Cookie.
Lava Cookies cure Pokémon of all non-volatile status conditions, but these items aren’t something you’ll come across often on your travels. But one can be located on Route 213.
When you reach Valor Lakefront, towards the back of the town, you can find a blonde lady standing outside a hotel. If you speak to her, she will ask you to help out finding a Suite Key. It can be difficult to find this item as there is no visual cue for its location.
Suite Key location in Pokémon Brilliant Diamond, Shining Pearl
After speaking to the womab, head south to Valor Lakefront’s entry on Route 213. As you walk through the reception building into Route 213, if you press “A” on the first block of the wall on your left, you should recover the Suite Key.
Now, simply take the key back to the lady awaiting entry into her room, and once you hand it over you’ll be able to enter. Enter the room and speak to her, and she will gift you a Lava Cookie for your help.
With this item, you can now head into battle knowing that you have another option to cure conditions that your Pokémon may be afflicted with during the duration of your battles.