Ghosts are creatures that haunt the town and the roads of Newbury. They originate from a spiritual world called "The Hidden Side" and are capable of possessing Humans and turning them into Gloombies. Most of them (e.g: Samuel Mason) were under the command of Lady E.
- Lady E. - Former leader of the Ghosts.
- Captain Archibald - Fused Ghost Pirate/Octopus.
- Samuel Mason - Fused spirit of Highwaymen Samuel Mason and John C. Newt.
- Dr. Drewell - Deceased scientist.
- Trucker Dale - Fused Ghost car thief/truck.
- Tragico - Three-headed Ghost clown.
- Maxine Turbo - Deceased Race Car driver
- Blaze M. Barr - Deceased Fireman.
- Spewer - Ghostly manifestation of trashed objects.
- Mr. Nibs - Ghostly Spirit that has taken on the form of Lady Evelina's Teddy Bear.
- Mamali - Lady Evelina's Ghost Nanny.
- Joe Ishmael - Deceased lighthouse keeper.
- The Maw - Ghost Golem.
- Bart Chaney - Criminal.
- Spencer - Jack's pet ghost dog.
- Magnus Gornason - Ghost Viking
- Anomalo - Ghost Chef/cockroaches fusion.
- The Bawa - Bat/Zombie train conductor.
- Harry Cane - Deceased inventor.
- Rat Shaun - Bank Robber.
- Kreatoru - Fused Ghost Scuba diver/Angler Fish.
Legendary ranked Ghosts are the most powerful Ghosts that a Hunter can encounter and thus, many of their members are used as Boss Ghosts in the App Game. Some require a Soul Artifact (Bosses), or a prized possession of the ghost when it was alive, and some do not (Mini Bosses). With massive health pools and the ability to fire large collections of gloom at their enemies, they will prove a challenge for any experienced hunter.
Rare ghosts are the least likely to be encountered by a hunter. These ghosts have a significant health boost from uncommon ghosts.
Uncommonly ranked ghosts are a bit less likely to be encountered by a hunter. These ghosts have a slight health boost in comparison to common ghosts.
Commonly ranked ghosts are the most likely to be encountered by a hunter. Common ghosts are, in most cases, the first rank of ghost that a hunter can catch.
They are able to possess individuals and turn them into beings called "Gloombies." Some Gloombies gain additional limbs when possessed by Ghosts, like either wings, a second pair of arms or four tentacles on their back. However, in the case of other Gloombies, they gain an additional head or even claw-like appendages.
The Ghost's main form of attack is Gloom. It usually comes in the form of a green slime ball but each of the three Ghost types have additional types of Gloom they can use when attacking their enemies.
- Anger Gloom comes either in the form of a red fire ball or just red Gloom.
- Sad Gloom comes either in the form of an electrically charged gloom ball or just blue Gloom.
- Wild Gloom comes either in the form of a yellow gloom mass that spreads into a volley of green Gloom balls when fired upon or just yellow Gloom.
- Ghosts usually haunt specific places based on their past life.
- The LEGO Life magazine claims that most ghosts hate salty food.
- In "Face Your Fears," Douglas was possessed by a Ghost whose name is currently unknown.
- Nagging Nathan, Wild Thomas, and Gary Atric's appearances are used for the common Ghosts seen in the different media of Hidden Side.
- A green ghost flies out of some former Gloombies, though green isn't the color of any ghosts.
- It is unknown if that is the color of ghosts after leaving a human's body, or if these ghosts are unique.
- Lil' Bo Pumpkins, Joe Snow, and Daisy are currently the only holiday themed ghosts in the app game. Bo being themed around Halloween, Joe around Christmas, and Daisy around Easter.
- The Duke is themed around summer, which isn't a holiday.
- Butch Lindenburger, Drew Jones, Madame Digamberetto, Daisy, Crooked Sven Robin, Monsieur Forte, Gary Linemann, Magnus Gornason, Cassius 'Blackeye' Sockem and Beau are currently the update ghosts who have a Legendary rank, but aren't Boss Ghosts.
- Originally, the app game listed the yellow ghosts type as the "Crazy" type. Now, however, it's known as the "Wild" type for unknown reasons.
- Diana appeared in two Hidden Side adverts and used to be in the app early on, but was deleted for unknown reasons. Later, she was added to the app in the 2020 Halloween update.
- According to the LEGO Life magazine, ghosts are easily distracted by cartoons.
- Only five ghost minifigures exist in the sets: Axel Chops, Scrimper, Waylon, Vaughn G. Jackson, and Spencer.
- Some concept art for another LEGO theme of Ninjago shows some ghost warriors with the same colors as those of the Hidden Side ghosts.