The protagonist of "Deep Trouble." Billy is a budding undersea explorer on vacation with his uncle, Dr. Deep, and his sister, Sheena. On the trip, he encounters a mermaid who he saves from kidnappers, and later goes on to have many more undersea adventures.
Adorkable: His constant optimism and awkward attempts at befriending the mermaid definitely fall under this.
Asian and Nerdy: According to the Horrorland spinoffs, he's asian american.
The Atoner: He spends the second half of "Deep Trouble" trying to make up for getting the Mermaid captured.
Badass Family: He, his sister, and uncle deal with sea based threats on a regular basis.
Cloud Cuckoo Lander: In the book's first few paragraphs, he criticizes Sheena for not opening her mind to concepts like the Easter Bunny and Santa Claus.
Friend to All Living Things: He makes fast friends with the mermaid, and claims that when he's a famous undersea explorer, he's going to give the creatures he encounters pet names. H also shows remorse about feeding a school of guppies to Dr. D's pet eel.
Fearless Fool: Not entirely fearless, but when his uncle warns him about sharks in the reef, he replies, "Sharks! Wow!" Later on, he rushes headfirst into a gang of thugs trying to kidnap the mermaid.
Straw Loser: Evan is one of the biggest ones in the whole series. He can not catch a break.
Lizzy and Luke Morris
The main characters of One Day In Horrorland
Cassandra Truth: Most of the Very Special Guests are not entirely trustworthy of the Morris siblings because they think they might be spies for the Horrors. It turns out however that of course Lizzy and Luke are the trustworthy ones. The twins Jillian and Jackson were unwittingly acting as The Mole for the Menace and attempted to make the Morrises as The Scapegoat. Lizzie realizes they've been trying to fool everyone when she catches Jillian lying.
The Leaders: Of the Very Special Guests in the last two books in the Horrorland series, due to their prior knowledge of the theme park.
Older and Wiser: Although they're only a year older in the HorrorLand series, they return to Horrorland to help out the rest of the kids escape.
Too Dumb to Live: Luke has shades of this in Return to Horrorland since he seems too eager to try out the rides at Horrorland despite the fact that he knows they are potentially lethal and that the Horrors tried to kill him and his family the last time they were there.
Villains and Monsters
Dark Falls Residents
The undead inhabitants of a remote town who lure new residents there to eat them.
Affably Evil: You wouldn't be able to tell their true nature until it's too late.
Anti-Villain: They feast on living beings to sustain their town's existence.
Almighty Janitor: Compton Dawes, Dark Falls' mild mannered real estate agent, is not only a bloodsucking mutant, but he's also the most responsible for keeping the town alive.
A Fate Worse Than Death: Little Karen Somerset (and presumably other residents) thinks this way of her undead existence.
Once a normal young girl staying at "Camp Cold Lake", Della grew tired of the constant safety rules and became homesick. She attempted to swim across the lake to leave camp, but she drowned. Now her lonely spirit roams the camp, desperate for a buddy to take her to the afterlife. She actually tried to leave by going through the woods, but was bitten by a rattlesnake. She made Sarah Maas think she drowned as part of a ploy to lure her into the woods and kill her there.
Anti-Villain: A little girl who is willing to do anything to make a friend, even murder.
And I Must Scream: Her ghost spent years wandering the camp, unable to leave the mortal plane.
Ax-Crazy: Veers more and more into this after Sarah rejects her, even trying at one point to run her down with a motorboat.
Broken Bird: Being trapped for years in a place you hate and getting rejected by those you want as friends will really do that.
Cute Ghost Girl: When she's not trying to stalk and kill you, she's actually rather friendly, giving Sarah a coat when she was cold.
Despair Event Horizon: After Sarah makes her refusal clear, Della wails in misery and sinks into the ground.
Manipulative Bitch: Pulls off a vicious gambit where she makes Sarah terrified of the water by pretending to have drowned, so that she can find her when she least suspects it.
Family-Unfriendly Death: Disposes of his clone by chopping him in half. Even worse, he did it in full view of his children.
Four Eyes, Zero Soul: Subverted. He's not really evil, just stubborn and willing to ignore certain morals.
Genetic Memory: His clone went rogue because of this-since he was a near perfect copy of the original, he had all of that man's memories.
Humanity Ensues: What made him think turning plants into humans was a good idea?
Kill and Replace: His clone was presumably planning this, both for him and the rest of his family.
LEGO Genetics: Apparently,combining plant and human DNA only took him a few weeks.
Mad Scientist: His freakish experiments with plant matter are what causes the book's conflict.
Nice Hat: An LA Dodgers cap, which covers the leaves on his scalp.
Plant Person: He spent hours in his basement trying to create these. Unfortunately for his family, he succeeded.
The Workaholic: Spends hours in his basement trying to perfect his experiments and ends up sorely regretting it.
A living halloween mask, one of several created by a scientist.
Ascended Extra: In the book The Haunted Mask II, the Mask wasn't featured at all. In the television adaption, the Mask is added to the plot as the main villain, possessing the shopkeeper and turning Steve into his minion for the sake of getting to Carly Beth and possessing her again.
Noodle Incident: No explanation is ever given for how he came to the real world.
Pick on Someone Your Own Size: Toward Skipper. His insane logic is that since this kid knows everything about him while the heroes of his world are complete idiots, he'll make a perfect opponent. Surprisingly enough,he was right.
Worthy Opponent: To a degree. He takes time to explain what's going on to Skipper so he won't die too confused.
The librarian of Dark Falls and the main antagonist of The Girl Who Cried Monster. Although he looks like a normal, albeit slightly overweight, human, Mortman is actually a monster who eats insects, reptiles, fish... and sometimes people.
Bald of Evil: He's described as having male-pattern baldness, and appears this way in the TV episode as well.
Four Eyes, Zero Soul: Although the actual book never mentions him wearing glasses, the cover art shows him with a pair, and the TV episode followed its example.
G-Rated Drug: Although it's not treated like one, a formula that causes massive growth would probably be the ultimate performance enhancer.
Generic Doomsday Villain: This is to be expected, since it's a mindless lifeform, but it's creator, Sarabeth, is a more straightforward example. Other than wanting to keep Evan's aunt as a slave, she has no personality or motivation whatsoever, and is simply in the story to provide an explanation for the ever growing slime.
The Big Bad of the "Night Of The Living Dummy" series of books and currently the one reoccurring character to appear in the most books.
Ascended Extra: Didn't come to life until the very end of Night of the Living Dummy, after the heroes destroyed the main antagonist, Mr. Wood. The sequels obviously focus on Slappy, though he occasionally shares the spotlight with other dummies.
I'm a Humanitarian: He orders the townspeople to cook Jessica for him after he turns her into a pig girl.
Karma Houdini: He escapes the destruction of Karlsville unharmed and can't believe his luck.
Laughably Evil: His idea of fun is to torment and kill kids with deadly pranks.
Manipulative Bastard: He manipulates Jessica into pursuing her greed, then blames her for the flaw he himself set her up to pursue, and turns her into a pig.
Reality Warper: In Karlsville his powers have almost no limits. He transforms Jessica into a pig girl, materializes minions out of thin air, and controls even the weather in the city. Fitting, since he's basically an evil Looney Tunes character.
Would Hurt a Child: He only seems to target children, trying to kill one in every episode.
Billy and Sheena's uncle, he's a marine biologist who discovers all sorts of strange phenomena that endanger him, his niece, and nephew.
The owner of a mask shop in The Haunted Mask. Also appears briefly in The Haunted Mask II. He creates masks of living flesh to conceal his own deformities (see All There in the Manual below) but they always become corrupted and ugly, forcing him to keep making new ones. In the Goosebumps TV series, he's played by Canadian actor Colin Fox.
Adaptation Expansion: In the TV episode of The Haunted Mask II he has a greatly expanded role, wherein he gets taken over by the original Haunted Mask.
All There in the Manual: His backstory is provided in the Goosebumps Collector's Caps Book, wherein it's revealed he was injured in a high school chemistry accident, leading him to begin creating the masks.
Dark Is Not Evil: Despite his all-black attire and generally slightly threatening manner, he isn't that bad of a guy, just sort of moody and depressed.
Reed Richards Is Useless: The pioneering this guy did in growing artificial, lifelike faces would have ended disfigurement, had he taken the time to publish his discoveries.
Dr. Deep's assistant. A nice guy, but a terrible cook. After his boss captures the mermaid, Alexander decides to steal it for himself and make a fortune. He's last seen under attack by the creature's vengeful family.
Asshole Victim: He was willing to murder children just to strike it rich. Needless to say, no one's complaining when the mermaids drag him to his doom.