Ghosts in the Pokémon world
Ghosts (Japanese: ゆうれい ghost) are souls that live in Lavender Town's Pokémon Tower.
In the games
In the games, before getting a Silph Scope, several unidentified ghosts (namely Gastly, Haunter and Cubone) appear. Later, another ghost is revealed to be a mother Marowak killed by Team Rocket. Therefore, it now haunts the Pokémon Tower.
Without the Silph Scope, the ghosts are impossible to battle. Whenever the player orders an attack against the ghost, the message comes up "(Pokémon) is too scared to move!", and instead of attacking, the message comes up: "Ghost: Get out.... Get out....". Before the battle against Marowak's ghost, a similar message appears, saying "Be gone... Intruders..." If one tries to throw a Poké Ball at a ghost, it dodges it, and the message comes up "It dodged the thrown Ball! This Pokémon can't be caught!". This also happens with the Marowak's ghost, before or after unmasking it. Even Master Balls fail to capture the ghosts.
The player eventually needs to defeat Giovanni in Celadon City's Rocket Hideout and get the Silph Scope, an item made by Silph Co. that makes ghosts visible. After the Marowak has been defeated, several Team Rocket Grunts that are "talking" with Mr. Fuji about that they killed it must be battled. In Generation II, Mr. Fuji created Lavender Volunteer Pokémon House for the same reason as Pokémon Tower, after the tower become the Kanto Radio Tower. The ghost itself is uncatchable.
The ghost is also related to two glitches. One of them is the fact that the sprite is used as one of Missingno.'s forms in Generation I, while the other is that it can be battled as a normal Pokémon by walking through walls in Generation II.
In Red, Blue, and Yellow, there is a glitch that one can exploit to make the ghost reveal itself. In battle, simply check the stats of any Pokémon. Then return to the battle. The ghost will turn into either a Gastly, Haunter, or Cubone. This has no other effect, though, as it still cannot be battled. Also, if the Silph Scope is deposited in the PC, any Ghost Pokémon during battle will be "too scared to fight."
In the anime
In the anime, a ghost of the same sort appeared briefly in The Tower of Terror. It even had Pokédex data, though that data simply said that it was missing data. Later, a Haunter takes Ash's and Pikachu's souls out of their bodies after they have been killed by a chandelier. Here is it shown that ghosts can fly around and remain in the form they took while living, however, with the exception that living beings cannot see them.
