Ghosts

Ghosts are spirit beings that were once physical living beings. They remain somehow attached to the physical world after their original forms have passed away.

Mainstream Smurfs Media
The Smurfs have encountered various types of ghosts. One of them was a nightclub entertainer and musician named Ghostwriter, who provided Harmony Smurf an "original" symphony that the Smurf musician can claim as his own in exchange for being that ghost's eternal performer at his nightclub. Papa Smurf contested that claim by having his Village Smurphony Orchestra play the entire "original" symphony, which was revealed to be pieces of other musicians' works that Ghostwriter was infringing upon.

In Quarrel Castle, Peewit ran into the ghost named Uncle Fenwick, who at one time had relatives paying him a visit to celebrate his Ghost Day.

In the comic books, a few Smurfs met a little ghost who hid himself inside a box in The Old Tower because he was too ashamed of his inability to frighten people. When Gargamel paid a visit to the tower to look for Smurfs, the little ghost tried to scare Gargamel away, but unknown to the little ghost it was really Puppy who chased off Gargamel.