- Adam Freeman - The leader of the gang who is relatively new to Spooksville.
- Sara "Sally" Wilcox - A pessimist girl who often tells of gruesome history of Spooksville and predicts any horrible ends to the gang if they are in a dangerous situation
- Watch - A very intelligent boy with an extensive knowledge of basic subjects.
- Cindy Makey - Also new to Spooksville as she and her family moved into her father's old house after his tragic death. Cindy also had a crush on Adam but is now beginning to think that Bryce is more worthy of her affections
- Bryce Poole - A great protector of Earth who deals with great cosmic emergencies and other major crisis.
- Ann Templeton - The local town witch of Spooksville, whom the gang often come to for advice about how to stop any danger they are unable to handle. She is the descendant of Madeline Templeton.
- Bum - The former mayor of Spooksville, who also helps out the gang on their quests.
- Mr. Patton - A brave man and an ally of the gang who owns an Army Surplus store in town and often provides heavy-duty weapons for the gang to defeat their enemies in spite of their age.
- George Sanders - A boy who is also new to Spooksville. He is somewhat of a coward and scared of his own shadow but he does help Adam and his friends out on some of their endeavors, such as when Mr. Snakol was planning to take over Earth.
- Tira Jones - A hundred-year-old girl with the body of a twelve-year-old, who was once possessed by a No-One, making her immortal. She has become an ally to the gang and now lives with a foster family.
- Evelyn Makey - Cindy's grandmother, whose son Frederick was swept away by the ocean and found elsewhere later. Evelyn died and returned as the vengeful spirit in The Howling Ghost that abducted Neil Makey, who, unbeknowst to either party at the time, was her grandson. She has since passed on to the other side as a spirit following the events at the lighthouse.
- Ekwee12 - A young alien who helps the gang escape from the evil teachers that have kidnapped them to put on display. He and his people are then revealed to be from Earth and they are humans from the future who have been changed from evolution.
- Pan - A half-human, half-goat creature, who lost his kingdom to an evil wizard named Klandor after losing in a gambling game on his birthday when Klandor made him wear a necklace that had the power to make him see what wasn't. He soon got his kingdom back when Watch won a gambling game with Klandor himself when he made the wizard wear the same necklace.
- Sarshi - A ten-year-old fairy who is quite powerful for her age and is a strongly loyal subject to Pan.
- Sara - A brontosaurus that Bryce managed to befriend and tame to assist them against the invasion of the other dinosaurs. Bryce also named her after Sally.
- Traelle - An alien that went into the prehistoric times that helped the gang stop an atomic bomb that caused an opening between the prehistoric times and the modern world.
- Mr. Castro - Middle school history teacher who, according to Sally and Watch, is a robot who is either from the North or South Pole or from the future. He has "several machinelike qualities": he purportedly never eats lunch or drinks water, lays out on the football field to "recharge his batteries", and wears a hearing aid that resembles a cosmic receiver and "is wired directly into his positronic brain". Sally also claims that he removes his eyeballs to clean his contact lenses.
- Mrs. Fry - Biology teacher
- Barbara and Betty Blue - A pair of conjoined twins who were dressed as a fortune-teller and were one (or two) of the trick-or-treaters that were trapped in The Evil House. They helped the gang throughout their journey in The Evil House.
- Teddy Fender - A boy who had dressed as Wild Bill for Halloween and was one of Marvin's thugs in The Evil House.
- Judge Jeff Poole - Bryce Poole's ancestor who had sentenced Madeline Templeton to death for her sorcery. He was accidentally killed during the time Adam and Sally went back in the time of Madeline with the Time Figure, which affected the Poole family line terribly. Watch managed to fix it by going back to the moment the gang have found the Time Figure and took it before their past selves could find it.
- Tweek - A young boy from the future who joined Watch and Cindy to save Adam and Sally when they were in the time of Madeline Templeton. At first he was awestruck that he was going with his idols on his birthday, but then he later regretted his decision.
- Zeta - A young elfish-looking boy that lives Centrae, the capital of Cetine and is the nephew of King Furma. Cindy befriended him after he saved her from a Shadow that brought her into their world and she managed to teach him good manners.
- Clere - Zeta's girlfriend, who helped her boyfriend and the gang escape when they were imprisoned and managed to alert their people of the terrible alliance that was formed.
- King Furma - Zeta's uncle and the High Lord of all Cetine. He once tried to help his people by forming an unlikely alliance with the Shadows to defeat the people of Gilbrare, who have been questioning and defying his authority. He finally saw sense after his nephew talked to him of the fatal danger and when the Shadows were defeated.
- Prince Tomel - A character from the story called The Emerald Sun who had put a curse on Watch in order to cure Princess Rula of the curse Xeto had placed on her.
- Princess Rula - The princess from The Emerald Sun who was cursed by Xeto after Rula accidentally killed her father.
- Xeto - A sorceress who had placed a curse on Princess Rula as revenge for killing her father. She later regretted her decision after Watch's untimely "death".
- Olos - Dr. Dee's "daughter" who tries to help her "father" by leading the gang to him and their people, the Pith to help fight their enemies, the Triton only to find that they have lost the war and her father had to sacrifice himself and their people to save their world. After that Olos was revealed to be a robot created by Dr. Dee when the XH killed her. Adam was falling for Olos in spite that she was a robot and was heartbroken when she died.
- Dr. Dee - Olos' "father" who was the leader of his creations, the Pith. He also created Olos as well. After his people have lost their war against the Trition, he sacrificed himself and them to save their world, but not before allowing Olos to escape with the gang.
- Tad - A talking spaceship, whom Bryce wished for after being granted one by Ann Templeton.
This list details characters who have suffered some form of supernatural, paranormal, or otherwise unpleasant phenomenon in Spooksville. Most of the stories of these characters come from Sally, who frequently exaggerates the truth, and few have been witnessed first-hand, so their authenticity cannot be verified.
- Leslie Lotte - A girl who was supposedly swallowed up by the sky while flying a kite in the park, as told by Sally. Watch later corrects that he saw her get lost in the fog and that no one could find her, and that she may have run away.
- Old Man Farmer - A man who was fishing in the town reservoir when a spacecraft hovered over him and shot a beam of vibration at him, which turned him into an alien. He later reverted back to normal, with the exception of a pointed chin.
- David "Jaws" Green - A boy whose right leg was bitten off by a shark near the shore/close to the jetty of the ocean.
- Bill Balley - A photography nut who explored the cave from The Haunted Cave; went missing, and all that was left of him was his camera, covered in what may have been blood or peanut butter and jelly, that contained a few shots of a mysterious, hairy creature.
- Danny Child - A boy who bragged about papering the Witch's castle. Ann Templeton raised the plank on him, causing him to fall into the moat. He was presumed to have been eaten by the crocodiles.
- Terry Falcon - A boy went to the hospital to have his tonsils removed, and instead had one kidney and his liver removed by the wstaff (who presumably sold the organs). It is implied that he is dead.
- Alternate Ann Templeton - An evil version of Ann Templeton who wants to collect body parts from her victims.
- Mrs. Robinson - An elderly agoraphobe who strikes fear in her victims.
- The Hyeets - Ape-like creatures who live in the Haunted Cave and they attack anyone who dares to enter the cave. They are also said to be the missing link between apes and humans.
- Ekwee12's teachers - Evil human aliens that have kidnapped Adam and Watch during what is said to be an educational trip to put on display.
- The Cold People - A group of icy creatures, who will stop at nothing to freeze many people, unless if there is fire present.
- Klandor - An evil wizard who stole Pan's throne by cheating in a gambling game with a necklace that had the power to make its wearer see what really wasn't, which he made Pan wear.
- The Pterodactyl - One of the dinosaurs that invaded Spooksville by going through the portal that was opened between its time and the modern world. It ambushed the gang and kidnapped Cindy to give to its babies.
- The Tyrannosaurus Rex - Another dinosaur that invaded Spooksville, which attacked Ann Templeton's castle.
- Mr. Snakol - An alien disguised as a science teacher who plans to take over Earth with his fellow species. He also likes to eat his students.
- Marvin the Magnificent - A hundred-year-old and cruel boy who ran a carnival that was beneath The Evil House and he imprisoned other kids while they were trick-or-treating by making them become the characters of their costumes and made them his slaves and believed himself to be the most powerful. He once used a book of spells that he borrowed from Madeline Templeton to help cure himself of a sickness that he had, which didn't work properly for him, therefore separating him from his ghost, who was waiting for a hundred years. Marvin was reunited with him after being convinced by Watch and Cindy and the other trick-or-treaters were free.
- The No-Ones - A race of ancient souls who are tired of being No-Ones and long to be somebody again, so they try to possess other beings to achieve this.
- The Shadows - A group of horribly savage monsters that live in the Forbidden Territories in Cetine, who are formed by everyone's fear. They have a terrible appetite for human brains and any one of their enemies. The things that destroy them completely are happiness and laughter.
- The Killer Crabs - A swarm of gigantic crabs that take Spooksville by storm.
- The Queen of the Vampires - The leader of a gang of vampires who wants to turn every living person into a vampire themselves.
- The XH - A blob created by Dr. Dee to multiply and take each of the kids' place while they helped in the fight against the Pith. But it turned out the XH had plans of its own and planned to kill the gang after they make their escape from the explosion that killed the Pith and the Triton.
- Neernitt - A vicious, power-hungry and self-aware computer consciousness that uses networking between computers to monitor human activity and uses various threats against the lives of humans to force them under its rule. In the end, after it was destroyed, Neernitt was revealed to be created by Savannah Stranger as a setup.