Secret Room

Secret Rooms are a feature that was added to the game in PMU 7. They appear in set floors throughout several dungeons and can be rarely found and accessed by stepping onto a hidden stairs tile.

Secret Rooms often rewards players with a varying amount of Deluxe Boxes that can give items when opened at Xatu's Appraisal. However, Secret Rooms may also allow players to spawn rare, exclusive Pokémon with Honey.

List of Dungeons with Secret Rooms
The following below lists the Dungeons that contains Secret Rooms and their corresponding information.

Exbel

 * Thunderstorm Forest and Far Thunderstorm Forest - 4 Boxes
 * Island Garden - 2 Boxes
 * Honeydrop Meadow - Scyther (Dawn), Pinsir (Dusk)
 * Gritty Hollow - 2 Boxes
 * Loch Lenile Cavern - Red Moon Spring (10F-19F), 2 Boxes
 * Mt. Barricade - ???
 * Southern Sea - 4 Boxes
 * Harmonic Tower - 3 Boxes (50F-74F), 1 Box and Bagon (75F+),

Winden

 * Winden Forest - ???
 * Sauna Cavern - ???
 * Snowveil Den - 2 Boxes
 * Mt. Stormhold - 2 Boxes
 * Sky Fortress Paths - 2 Boxes
 * Sky Fortress/Sky Garden - 4 Boxes

Tanren

 * Rocky Shoreline - Basculin
 * Sunken Gardens - 1 Box, Alomomola
 * Sunrise Temple - Larvesta egg
 * Tanren Mines - ???
 * Iceberg Cavern - Entrance to Iceberg Frigid Waters
 * Iceberg Frigid Waters - Clauncher
 * Iceberg Adrift - 2 Boxes
 * Daydream Dream Grove - 2 Boxes, Cresselia (31F+)
 * Nightmare Dream Grove - 2 Boxes, Darkrai (31F+)
 * Caustic Sewers - ???
 * Ancient Caustic Sewers - ???

Archford

 * Stark Volcanic Woods - Victini
 * Boggy Wastes - 4 Boxes
 * Starlit Lagoon - 2 Boxes
 * Inferno Volcano - 2 Boxes
 * Seafloor Ruins - 2 Boxes
 * Mysterious Jungle - 2 Boxes
 * Mt. Moon - 2 Boxes
 * Sandy Shallows - Pikachu
 * Murky Trench - 2 Boxes

Pokémon
In certain Secret Rooms it is possible to spawn Pokemon with Honey. The Pokémon that spawn in these rooms are often rare Pokémon only in these areas. The spawnable Secret Room Pokémon are as follows:
 * Scyther - Honeydrop Meadow (Dawn Only)
 * Pinsir - Honeydrop Meadow (Dusk Only)
 * Bagon - Harmonic Tower
 * Basculin - Rocky Shoreline
 * Alomomola - Sunken Gardens
 * Clauncher - Iceberg Frigid Waters
 * Cresselia - Daydream Dream Grove
 * Darkrai - Nightmare Dream Grove
 * Vullaby - Undercity Catacombs
 * Victini - Stark Volcanic Woods

In Sunrise Temple, the player can obtain a Larvesta egg after going through a puzzle. In Sandy Shallows, you'll meet a Pikachu who will then challenge you to a battle after the dialogue sequence and is recruitable. In 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 Phione.

Red Moon Springs
Red Moon Spring is a special Secret Room that was added to Loch Lenile Cavern. It serves a special purpose and a different layout then the common Secret Room. Instead of Deluxe Boxes or Honey Spawns that are found in other Secret Rooms, you regenerate Fossil Pokémon using Fossils.

The Fossils that can be resurrected in Red Moon Springs are as follows:
 * Helix Fossil (Omanyte) - Tanren Chambers/Water
 * Dome Fossil (Kabuto) - Crystal Ruins
 * Old Amber (Aerodactyl) - Mt. Skylift
 * Claw Fossil (Anorith) - Tanren Chambers/Bug
 * Root Fossil (Lileep) - Tanren Chambers/Grass
 * Armor Fossil (Shieldon) - Tanren Chambers/Steel
 * Skull Fossil (Cranidos) - Tanren Chambers/Rock
 * Plume Fossil (Archen) - Tanren Chambers/Fighting
 * Jaw Fossil (Tyrunt) - Dragon's Descent/Dragon's Descent Depths

When you summon the Pokémon via Fossil, the Pokémon will be at Level 25 recruitment rate of 100%.

Trivia

 * Secret Rooms only appear in randomly-generated dungeons. Fixed dungeons such as Friendship Forest will never have Secret Rooms.