There are many ways in which Gastly can be formed. Forming from the black cores of Shellder and Cloyster is the most common method, but most pokemon can become a ghost when their spirit is bonded too closely with the world of the living, and there are those among students of the magical arts who achieve immortality by turning into pokemon.
These students are commonly called magicians, but this is a broad description. Of the eight disciplines of magic, it is only the most skillful of illusionists who can turn into Gastly; even necromancers are unable. This is because Gastly itself are pokemon which specialize in this magic; their true bodies are invisible without the usage of special equipment or pokemon attacks. In the wild, they frequently play pranks with the usage of magical light, and many low-level stage magicians use Gastly (covertly) in their act.
The best magic shows in the world are delivered at the top of the Tower in Lavender Town. They are performed by the best illusionists who have died in the previous year alongside the greats of ages past. The audience is made up primarily of the dead, but a man or god by the name of Fuji is in attendance every year, and many devoted fans have snuck in over the years; some of them have even snuck out without being taken "back" to the afterlife with the rest of the audience.
As for the show itself, many have been asked to describe it, but few have even spoke coherently when making the attempt, and their accounts only agree in that it was the greatest thing they had ever experienced.
