Ghosts are most likely to appear as copies of previous-dead players in bones files, complete with their whole object assortment, and the pet may be nearby (feral). Any objects that were carried in the unfortunate player's main inventory have an 80% chance of becoming cursed, even if they were originally blessed. Other objects on the level and the contents of containers in the player's inventory maintain their BUC status.
When a player leaves a bones file, they leave a corpse and a ghost under regular circumstances. The ghost has the same experience level as the late player. If you use undead turning on the corpse the ghost will inhabit the player's corpse on the item pile, removing the ghost. The corpse can be of a polymorphed form if the target died while in another form, e.g. from wearing an amulet of unchanging. The ghost must be on or adjacent to the square the corpse is on. The ghost must be awake to be turned (the ghost is generated asleep). If the ghost is made tame, then the resulting monster will be tame if possible, otherwise the attitude of the resultant monster will be generated as normal (based on your alignment and race). The creature will also be confused upon recorporealizing, regardless of attitude. If successful, the message <Name>'s ghost is suddenly drawn into its former body! will be displayed.
Ghosts are very slow and do very little damage. However, they will probably evade all your hits if you meet them on a low level. If you can't kill them fast via regular attack, try kicking them instead.
By default ghosts and shades are represented by a blank space, making them difficult to see and almost impossible to locate by telepathy. Some players use the monsters option to give ghosts and shades a different appearance, such as X or 8. This makes them easier to see, and allows you to quickly identify bones levels via telepathy.
Ghosts of past players found in bones files will be named after the dead adventurer they represent. The ghost generated on the Rogue level will be named Michael Toy, Kenneth Arnold, or Glenn Wichman.
Ghosts created on other special levels have a 1/7 chance of being given your name. Otherwise, they will be given a random name from the following list:
And now the souls of the dead who had gone below came swarming
up from Erebus -- fresh brides, unmarried youths, old men
with life's long suffering behind them, tender young girls
still nursing this first anguish in their hearts, and a great
throng of warriors killed in battle, their spear-wounds gaping
yet and all their armor stained with blood. From this
multitude of souls, as they fluttered to and fro by the
trench, there came a moaning that was horrible to hear.
Panic drained the blood from my cheeks.