Secret Room

Secret Rooms are a feature that was added to the game in PMU 7. They are areas in dungeons that can be accessed through entering golden stairs found on a dungeon floor. These stairs have a random chance of spawning on a floor and initially spawn hidden. The floors a Secret Room can spawn on and the rate of appearance varies on the dungeon.

Not all dungeons have Secret Rooms, and Secret Rooms can only appear in randomly-generated dungeons. Fixed dungeons such as Friendship Forest will never have Secret Rooms. Secret Room stairs also cannot spawn on the last floor in a dungeon or its given section. Secret Rooms often reward players with a varying amount of Deluxe Boxes that can give items when opened at Xatu's Appraisal. However, some Secret Rooms also allow players to obtain rare, exclusive Pokémon.

Secret Room Pokémon
Secret Room Pokémon obtained through Honey:
 * Scyther - Honeydrop Meadow (Dawn and day only)
 * Pinsir - Honeydrop Meadow (Dusk and night only)
 * Bagon - Harmonic Tower
 * Basculin - Rocky Shoreline
 * Alomomola - Sunken Gardens
 * Clauncher - Iceberg Frigid Waters (Dawn and day only)
 * Cresselia - Daydream Dream Grove
 * Darkrai - Nightmare Dream Grove
 * Vullaby - Undercity Catacombs
 * Victini - Stark Volcanic Woods
 * Porygon - Concealed Laboratory
 * Female Meowstic - Starlit Lagoon
 * Dusk Form Lycanroc - Mystic Coven (Dusk only)
 * Midnight Form Lycanroc - Mystic Coven (Night only)

Secret Room Pokémon obtained miscellaneously:
 * Sunrise Temple - The player can obtain a Larvesta egg after going through a puzzle.
 * Tanren Courtyard - The player can use an Odd Keystone, only if it is night, on the stone well in its Secret Room to spawn a recruitable Spiritomb.
 * Tanren Graveyard - The player can use a Worn Doll on the sparkling tiles to spawn a recruitable Mimikyu.
 * Sandy Shallows - You'll meet a surfing Pikachu who will then challenge you to a battle after the dialogue sequence and is recruitable.
 * Central Seafloor Ruins - You can find a Secret Room wherein you can use Sea Dew to unlock a door leading to a platform to use a Wonder Egg and summon a recruitable Phione.

Dungeons With Secret Rooms
The following below lists the dungeons that contain Secret Rooms and their corresponding information.

Exbel

 * Island Garden - two boxes
 * Honeydrop Meadow - Scyther (Dawn), Pinsir (Dusk)
 * Far Thunderstorm Forest - two boxes
 * Gritty Burrow - two boxes
 * Loch Lenile Cavern - Red Moon Spring (11-20F), two boxes
 * Mt. Barricade - five boxes
 * Mt. Skylift - two boxes
 * Southern Sea - four boxes
 * Harmonic Tower - three boxes (50-74F), one box and Bagon (75F+)

Winden

 * Winden Forest - two boxes
 * Sauna Cavern - three boxes
 * Crystal Ruins - one box
 * Snowveil Den - two boxes
 * Mt. Stormhold - two boxes
 * Sky Fortress paths - two boxes
 * Sky Fortress Sky Garden - four boxes
 * Concealed Laboratory - Porygon
 * Risen Derelict - two boxes

Tanren

 * Rocky Shoreline - Basculin
 * Mystic Coven - Dusk Lycanroc (31-40F) (Dusk), Midnight Lycanroc (41-49F) (Night)
 * Sunken Gardens - one box, Alomomola
 * Sunrise Temple - Larvesta egg
 * Tanren Graveyard - Mimikyu
 * Tanren Mines - two boxes
 * Tanren Mines Depths - two boxes
 * Tanren Basement - four boxes
 * Tanren Courtyard - two boxes, Spiritomb (Night)
 * Iceberg Cavern - entrance to Iceberg Frigid Waters
 * Iceberg Frigid Waters - Lapras
 * Iceberg Adrift - two boxes
 * Deserted Tomb - two boxes
 * Dynamo Sands - two boxes
 * Daydream Dream Grove - two boxes, Cresselia (31F+)
 * Nightmare Dream Grove - two boxes, Darkrai (31F+)
 * Undercity Catacombs - two boxes, Vullaby
 * Ancient Caustic Sewers - two boxes

Archford

 * Stark Volcanic Woods - Victini
 * Boggy Wastes - four boxes
 * Starlit Lagoon - two boxes and female Meowstic
 * Inferno Volcano - two boxes
 * Seafloor Ruins - two boxes, Phione (Central)
 * Mysterious Jungle - two boxes
 * Mt. Moon - two boxes
 * Sandy Shallows - Pikachu
 * Murky Trench - two boxes
 * Shimmering Seabed - two boxes

Red Moon Spring
The Red Moon Spring is a special Secret Room in Loch Lenile Cavern. The player can regenerate Fossil Pokémon using Fossils when the time of the day is night.