Some of the best environments in the Pokémon series have been those underwater, but the games have sadly left them underused. Dive in the Gen 3 games and their remakes was a fun and unique mechanic that let players explore the ocean floor, which is one of the reasons why Hoenn is one of Pokémon's best regions. It hasn't appeared since, however, and future games in the series should bring this back in some form, including the upcoming Gen 9 games Pokémon Scarlet and Violet, releasing on November 18.
In Pokémon's Gen 3 games, Dive was an HM move taught by HM 08 in the original games and HM 07 in their remakes. In battle, it's a Water-type attack with a base power of 60 that will make the user invulnerable for one turn. Outside of battle, players can use it to dive deep beneath the water in certain places to explore a small area filled with Trainers, items, and wild Pokémon. Starting at Gen 4 onward, some Water-type Pokémon can learn it by leveling up, and it's appeared as a TM in Gen 8 that can be taught to even more, including some of Pokémon's best Water-type starters. It's also an HM in Gen 5, but it's not available until the post-game and is only used to access one area, the Abyssal Ruins.
As it currently stands, it doesn't appear that Gen 9's Scarlet and Violet will bring back Dive or any other underwater areas. Koraidon and Miraidon's aquatic traversal forms that allow players to navigate the surface of the water make anything below it seem unlikely, and there's been no mention of it in the various trailers that showcase its vast open world. However, this feature can still return in Gen 10 or a further game, and if Gen 5 gets remakes after Pokémon SV, they can vastly expand it from the original Black and White and their sequels, and let players catch their favorite Gen 5 Pokémon in an underwater setting.
Pokémon Should Bring Back Dive & Underwater Environments
In addition to the Dive areas in the mainline series, underwater environments have appeared in other Pokémon games such as Pokémon Snap and the Pokémon Ranger series. In every game, they have been unique and pleasing to the eye, and they have the potential to be even better in future ones given the increased power of the Nintendo Switch as opposed to handheld consoles that past games have been on as well as the better graphics that newer games have. If done right, they may even become the best environments the series has to offer.
Perhaps the greatest argument for the return of underwater environments in Pokémon's mainline series is the new direction it's been going in with the last few games. Pokémon Legends: Arceus had a semi-open world divided into sections, and Pokémon Scarlet and Violet are completely open-world with no restrictions, as opposed to the linear format the series has used in the past. The shift marks the perfect time for the return of underwater environments, as they can give players even more freedom and more places to explore, in addition to setting future Pokémon games apart from other massive open-world titles like Legend of Zelda: Breath of the Wild.
If underwater areas did return to Pokémon's mainline series, there are a few different ways they can be used. Even bringing back Hoenn's Dive areas with improved graphics and features could be great, but they could be even better if they were expanded to match the rest of the games' new open worlds. Underwater cave systems, coral reefs, and sunken ships could all be great to explore, especially with Water-type regional variant Pokémon and new evolutions to capture in them. Hopefully, Pokémon has plans to revive their underwater environments within the next few games, so that players can experience these and possibly more.