Ghost

Ghosts are the spirits of dead humans and other creatures that have not yet "passed on" to the afterlife. There are many theories as to why ghosts are said to exist, from remaining to sort unfinished business or simply hanging around to haunt people. Ghosts are characterised as being unable to touch anything, occasionally invisible, freezing cold and absolutely terrifying. Since there is no concrete evidence that ghosts even exist in the real world, they are wildly depicted in fiction.

Several ghosts (and poltergeists, a close relative to ghosts) have appeared within the pages of Sonic the Comic:

Ghosts are the main inhabitants of Ghost World, a separate world in the Wonder Boy series. Completely isolated from Monster World unless attached by floating steps, the main inhabitants are the residents of Dinotown, ferocious ghost dinosaurs planning on conquering all of the worlds. A few human ghosts can be found, such as Tom of Tom's Trading Post and Supply Emporium.

Fake ghosts were one of the obstacles in the Hell House Ride, a rollercoaster in the Carnival Night Zone designed by the Marxio Brothers. Chicio Marxio fired them into a tunnel to block the view of Knuckles the Echidna as he plummeted off the Floating Island. In reality, the ghosts are little more than sheets which are somehow able to move around.

Unpleasant ghosts inhabit the Lost Pyramid of Sandopolis, warding away any intruders who wish to steal the pyramid's vast treasures. These ghosts appear as small, globular spirits at first, but become more menacing the darker it gets in the room. They originally come from Sonic & Knuckles.

Filch is a poltergeist, a type of ghost that can manipulate items without touching them. He is Captain Plunder's right-hand lizard and leading member of the Sky Pirates.

The Ghost Ship of Tantaragor appeared to be an abandoned ghost ship floating in the skies of Mobius, but was actually a place for the Tantaror to keep their slaves. No ghosts lived here.

Sonic the Hedgehog and Tails once believed themselves to be up against ghosts on Verdant Hill, with Tails being particularly jumpy about the experience. In reality, the "attackers" were just inter-dimensional travellers who had bought a faulty ship from Honest Lew's Budget Dimension Travel.

The Skeleton Crew are a group of trouble-making ghosts and skeletons from the Grim Dead Zone that only appear at Hallowe'en every 50 years.

A manipulation by the Ring of Eternity convinced Amy Rose that the ghost of a massive monster was rampaging through the Snowcap Mountain Zone.

Many ghosts run rampant throughout the Haunted Hill Zone. The biggest of them all, King Boom Boo, can be summoned with an hourglass summoned by Rouge the Bat, but they will all lose interest if there is nobody to command them. The area shares a similarity with the site of the Temple of Tikal and Vichama's Temple, as the ghosts are all fallen warriors; the difference is whether they are members of the Drakon Empire or echidnas from Megopolis City.

Ghost Robotnik is a spirit version of Doctor Robotnik, presumably the fate that awaits the current Robotnik should he die. This tyrant was summoned by the Pirate Omni-Viewer to fight several Sonics alongside many incarnations of himself in Many Happy Returns.