
This is a big change from Pokémon Diamond and Pearl's original Underground, which didn't feature areas for players to catch or encounter wild Pokémon. These areas, which have several similarities to Sword and Shield's Wild Areas, come in a variety of biomes and appear to spawn a variety of Pokémon based on the biome type.

While the tunnels of the original Underground remain, the Grand Underground also features Pokémon Hideaways, special biomes with overworld spawning Pokémon for players to capture. Pokémon Brilliant Diamond and Shining Pearl have taken the foundation of Diamond and Pearl's Underground and expanded the idea to a fully explorable world under the Sinnoh region. Related: Pokémon Evolutions' Art Style Would Be Perfect For A Pokémon Game It was not only a fun feature during the game's main storyline, but added post-game content, with hours of exploration possible. The Underground seemed to be a mixture of the Secret Base mechanic from Ruby and Sapphire, and the concept of the Dive HM, which in the Hoenn region allowed players to dive under the ocean to explore underwater maps and caves for items. Returning mechanics from Pokémon Ruby and Sapphire, like Pokémon Contests and berry growing, were fleshed out with new gameplay in Diamond and Pearl, as well as the addition of areas like the Sinnoh Underground. Originally released in 2006 for the Nintendo DS, Pokémon Diamond and Pearl introduced numerous concepts to help expand gameplay from previous titles in the series. However, Brilliant Diamond and Shining Pearl have expanded on the original concept of the Underground, introducing the Grand Underground, with new features to reinvigorate exploration in the upcoming remakes. With the use of an Explorer Kit, players could travel underneath the region searching for rare items like fossils and evolution stones, while building secret bases to hide flags for co-op rounds of capture the flag with friends. In the original Diamond and Pearl, the Underground was an expanse of tunnels running like a grid beneath the Sinnoh region. Big changes have been made to Pokémon Brilliant Diamond and Shining Pearl'sunderground mini-game location.
