Mossdeep City

Main article: Mossdeep Space Center

Mossdeep was the ideal location to build a space center which launches huge rockets because of the stable weather conditions. The Space Center is successfully sending rockets into space. In Emerald, the Space Center plays a big part in the plot, where Team Magma attempts to steal rocket fuel while a rocket begins to launch into space. On the second floor, the player will meet with Steven and battle two Team Magma Grunts.

The Space Center also plays a key role in the Delta Episode of Omega Ruby and Alpha Sapphire. A Kecleon hides behind the astronaut cut out on the bottom floor in after the Delta Episode. This Kecleon has its hidden ability Protean.

The possibility of rare stones in the cavern has attracted the attention of Steven Stone, who owns a cottage here where he keeps part of his rock collection. He will leave behind a rare Beldum after the player enters the Hall of Fame. Steven will also give the player HM08 here in Ruby and Sapphire (HM07 in their remakes, both containing Dive). In Emerald, however, he will give the player HM08 after defeating Team Magma at the Space Center. In Omega Ruby and Alpha Sapphire, Steven's collection includes hornblende biotite granite from Rock Tunnel, pitchstone from Mt. Mortar, chert from Mt. Pyre, schalstein from Mt. Coronet and greenschist from Chargestone Cave.

The house west of the Pokémon Center houses a brother and sister. The boy likes to visit people's Secret Bases.

In Pokémon Ruby, Sapphire, and Emerald, the boy will tell the player where their Secret Base is located.

In Pokémon Omega Ruby and Alpha Sapphire, the boy tells the player that they can access additional areas in Secret Bases with Stairs and Solid Boards.

The house north of the Pokémon Center houses a couple. The man is a Black Belt who is very enthusiastic about Pokéblocks.

In Pokémon Ruby, Sapphire, and Emerald, he will tell the player the preferred color of Pokéblock of the player's lead Pokémon.

In Pokémon Omega Ruby and Alpha Sapphire, he serves no purpose, simply telling the player that their lead Pokémon likes them more than Pokéblocks.

In Pokémon Ruby and Sapphire and Pokémon Omega Ruby and Alpha Sapphire, these is an old man with a house with a door on the back wall.

In Pokémon Ruby and Sapphire, e-Reader Trainers will appear in the back room.

In Pokémon Omega Ruby and Alpha Sapphire, the old man mentions he used to be a Secret Base Expert. If the player scans the QR Code of a special Secret Base (such as those of Junichi Masuda, Shigeru Ohmori, Shigeki Morimoto, and Shōko Nakagawa), it will appear behind this door.

A Game Corner is located here in Pokémon Emerald. It replaces the backdoor house from Pokémon Ruby and Sapphire. It allows players to interact with Pokémon FireRed and LeafGreen and other copies of Emerald in two mini-games, Pokémon Jump and Dodrio Berry Picking. Connections are made with the Game Boy Advance Wireless Adapter.

Visit the house nearest the stairway to the Space Center to meet a young woman who uses a Wingull to send letters to a friend in Fortree City. Talk to the Wingull and it will take flight, off to deliver another note. If the player return to Fortree and visit the Pokémon Breeder in the northeast house there, it will get a Mental Herb that his Wingull found in its travels.

In Pokémon Emerald, there is a Black Belt on the shore in the western part of the city who will teach a compatible Pokémon DynamicPunch one time only.

Main article: Mossdeep Gym

The Mossdeep Gym is Mossdeep City's official Pokémon Gym, which specializes in Psychic-type Pokémon. Its Leaders are Tate and Liza, who are faced in a Double Battle. Defeating them earns the player the Mind Badge and TM04 (Calm Mind).

In Pokémon Ruby and Sapphire, the population of Mossdeep City is 45. Despite it being on an island in the middle of the sea, its population is fairly large, and it is Hoenn's fourth most populous city.

In Pokémon Emerald, the population of Mossdeep City is 52, making it Hoenn's fourth most populous city.

In Pokémon Omega Ruby and Alpha Sapphire, the population of Mossdeep City is 45, making it Hoenn's fifth most populous city.

Ash and his friends arrived in Mossdeep City in It's Still Rocket Roll to Me! and immediately found the Mossdeep Gym. However, it was temporarily closed due to a space shuttle launch, so the group followed Rachel to the Mossdeep Space Center, where they met up with the local Gym Leaders, Rachel's twin children Tate and Liza. The two groups worked together to foil Team Rocket's plan to steal the space shuttle.

In Solid as a Solrock, Ash battled Tate and Liza and won, claiming his seventh Hoenn League Badge.

In Dreams of the Sun and Moon!, Sophocles mentioned that he had plans to visit Mossdeep City and the Mossdeep Space Center with Molayne during the upcoming vacation. They departed for said vacation in the next episode. In That New Old Gang of Mine!, Sophocles was revealed to have returned to Alola from his trip, although he was planning to visit the Space Center again in the future.

According to the anime, Mossdeep City is located on Mossdeep Island. As mentioned in Judgment Day! and Clamperl of Wisdom, ferry services run between Mossdeep and some of its neighboring islands, as well as Lilycove City.

Mossdeep City in Pokémon Generations

Mossdeep City made a couple of brief background appearances during The Cavern. It also briefly appeared in The Scoop, with the episode's focus being mainly on the Mossdeep Space Center.

Mossdeep City was the setting of two flashbacks. In the first flashback, Steven arranged a meeting in his house with Ruby and Emerald, where the two learned about a meteor's impending impact with their planet. After telling the two about his father's plan and their awareness of opposition to it, Steven also gave Ruby and Emerald a Mega Bracelet each, as well as an additional Mega Bracelet to pass to Sapphire. In the second flashback, Ruby and Emerald were at the Mossdeep coastline after their meeting with Steven. Ruby then used Courtney's memory lighter to investigate Steven's potential enemy.