From Glitch City Laboratories
The See a Ghost without a Silph Scope glitch allows the player to see the true form of a ghost in the Pokémon Tower. Although through the use of this glitch, the player can see the Pokémon the ghost actually is, he or she cannot catch or battle this Pokémon without a Silph Scope.
1. Go to the Pokemon Tower in Lavender Town.
2. Have a Ghost battle the player.
3. Go to "PKMN", select one of them and choose "STATS"
4. Go back to the Battle screen, and the player will be able to see the Ghost's real form.