When players enter the Grand Underground in Pokemon Brilliant Diamond and Shining Pearl or BDSP, the game will give them a Digger Drill item. This item allows players to warp out of the caves at any time by pressing Y. This will bring up a menu that gives players two options: Grand Underground Map or Go Up.

While in the Grand Underground, players can collect a variety of items that cannot be found elsewhere. These include gems, rocks, plates, fossils, evolution stones, and even statues. The easiest way to collect these items is by finding a digging spot. These can be spotted as yellow dots on the Grand Underground map. Then, by using the Digger Drill, players can start a digging minigame that can result in these rare finds.

Players can also keep track of their progress in the Grand Underground by looking at a meter underneath the Grand Underground map. This meter starts at 0 and maxes out at 40. Players can add to this meter by running into Diglett or Dugtrio while in the Grand Underground, with each encounter adding 1 to the metre.

However, the meter will reset every time players leave the Grand Underground. Therefore, if players are close to reaching 40, they should make sure to not leave or else it will start over again. Additionally, the chances of encountering Shiny Pokemon in the Grand Underground are higher if the metre is at 40 or above.