The Pokémon Mansion has four different floors. Doors can be unlocked in the mansion by pressing switches hidden in statues scattered around the building. In Generations I and III, there is a balcony on 3F with two possible points to jump down from, with the eastern one leading back to 2F and the western one leading to 1F and allowing the player to access B1F, while in Generation VII, the western balcony is the only possible way down, and it is utilized by climbing down a ladder instead of jumping. In Generation VII only, there are beds at the basement, which the player can rest in, fully healing their entire party. In Generations I and III, there is an exit at the southeast corner of 1F, which transports the player back to the front door of the mansion, while in Generation VII, it is replaced by a one-way warp panel that serves the same purpose.
Amongst the rubble and wreckage are journal entries written by the scientist who obtained a Mew and cloned it to create Mewtwo. In Generation VII, there are also multiple glass containers likely used during said cloning process at the basement, the largest one of which shows signs of having been beaten on over and over from the inside.
The Pokémon Mansion, along with every other building on Cinnabar Island, is destroyed in the eruption of the Cinnabar Island volcano prior to the events of Generations II and IV, and as such, it no longer exists.
Red was seen visiting the Pokémon Mansion in File 3: Giovanni. The Mansion used to be full of different kinds of Pokémon, but was now just an old, abandoned house. While exploring the Mansion, Red found a journal describing the discovery of a new species of Pokémon.
The Pokémon Mansion was also referenced in File 4: Charizard, where Red recalled reading the entries in the journal, leading to him identifying the Pokémon Blue had recently fought against and lost to as Mewtwo, possibly created in the very same Mansion Red visited and found the journal from.
In Generation VII, if the player brings a Mew or Mewtwo along as the walking Pokémon towards the cloning area of Pokémon Mansion, it will stop and stare at the largest cloning container, and interacting with it will have the dialogue box state that it is staring quietly at the machine.
In Generation I, it is possible to get stuck on 3F. This happens if the player stands on the east side of the table in the southwestern room and the Burglar with a Ninetales then challenges them to a battle. After the battle, the player will be stuck in a corner, the Burglar blocking the way. If the player saves after this and doesn't have an Escape Rope or a Pokémon with Dig, the only way to escape is to white out by fighting wild Pokémon. The layout was changed in FireRed and LeafGreen, and it is no longer possible to get trapped.