Lindy is a seven-year-old girl who initially struggles with ordinary childhood fears, such as knocking on the door of the supposedly haunted Stone House. She occasionally sucks her thumb, a habit her older brothers tease her about. Despite her youth, her active imagination makes her an ideal candidate for Samuel Savant's training. She possesses a sensitive disposition and frequently cries, but she channels her emotions into bravery when facing dangerous situations.

Samuel Savant is an esteemed biology professor and geneticist who recently won the Nobel Prize. He lives in the supposedly haunted Stone House in Bramblewood, where he prefers isolation to focus on his scientific research. Despite his strict scientific background, he believes wholeheartedly in magic and claims to know how to reach the last remaining Whangdoodle. He actively trains the Potter children to observe the world around them using all their senses.

The Prock is a tall, exceedingly thin creature who serves as the prime minister of Whangdoodleland. He takes his duty to protect his country seriously, viewing human beings as threats due to their history of violence. To deter Savant and the Potter children from reaching the king, he deploys various beasts and traps. He can vanish into cracks in the floor and manipulate situations to cause fear and confusion.

The Whangdoodle is the king and last surviving member of his species, residing in a crystal palace in Whangdoodleland. He has the body of a small pony, large handsome antlers, and grows his own bedroom slippers. He possesses a strong sweet tooth, enjoying treats like wodge candy and ice cream, but suffers from deep loneliness. He relies on his prime minister to keep his borders secure from humans, whom he deeply distrusts.

Ben is the thirteen-year-old eldest sibling of the Potter family. He tries to act responsible and level-headed, keeping a close eye on his sister when she accepts a scary Halloween dare. Because he is the oldest, he finds it slightly harder to unlock his imagination during Savant's sensory exercises. He often acts as the voice of reason when his younger brother starts arguments.

Tom is the ten-year-old middle child of the Potter family. He has an argumentative streak and frequently bets with or teases Lindy. When he first hears about the Whangdoodle, he looks it up in the dictionary and dismisses the creature as a phony invention. However, he joins the expedition and applies himself to the professor's training, learning to focus his mind on his surroundings.

The Whiffle Bird is a colorful, silky creature native to Whangdoodleland. She acts as a guide and early-warning system for travelers, swooping in whenever danger approaches. Instead of speaking plainly, she yells out phrases like "Mayday!" or offers cryptic idioms that the group must interpret literally to survive the journey.

The Splintercat is a mountain-dwelling feline who resembles a cross between a kitten and a mountain lion. His hind legs are longer than his front legs, causing his rear to stick up in the air. He enjoys playing games like cat's cradle and uses flattery to manipulate others. He works under orders to stop the humans from progressing further into the country by distracting them with sweets and games.

Mr. Potter is a university professor in Bramblewood and the father of Lindy, Tom, and Ben. He requires a quiet house to prepare his lectures, which prompts his wife to send the children to the zoo. He encourages his children to act responsibly and values scientific education.

Mrs. Potter is the mother of Ben, Tom, and Lindy. She listens to her daughter's fears about the haunted house dare and offers practical advice, suggesting Lindy talk to her older brother for comfort. She is thrilled when a famous Nobel Prize winner takes an interest in tutoring her children.

Mrs. Primrose is the domestic helper who works at Stone House. She prepares hot chocolate and snacks for the children when they visit for their regular training sessions with the professor.

Ethel is the domestic worker employed by the Potter family. She supervises the children during their midterm holiday, allowing them the freedom to spend their days studying with the professor at Stone House.

The Gyascutus is a massive, aggressive bird that patrols the skies of Whangdoodleland. It guards the rainbow bridge leading to the royal palace, attempting to hook intruders with its sharp talons to prevent them from crossing the chasm.

The Sidewinders act as the private security force of Whangdoodleland. They possess five legs and heavy bodies shaped like cannons. They attempt to frighten intruders but collapse into a heap if someone stands their ground and startles them directly.

The Swamp Gaboons are green, apelike creatures who thrive on generating anger and frustration. They verbally harass passersby, attempting to provoke a violent or emotional reaction. If their targets ignore them or respond politely, the Gaboons become desperate and throw tantrums.

The Tree Squeaks are monkey-like creatures that live in the forests of Whangdoodleland. They have the ability to sleep with their eyes open. When awakened, they emit horrible, continuous screeching sounds that alert the entire area to intruders.

The Oinck is a confounding creature whose primary purpose is to confuse travelers. He provides unhelpful or painfully obvious directions disguised as riddles, attempting to slow down anyone heading toward the royal palace.

The Gazooks are deceptive creatures that camouflage themselves as mechanical objects. When someone sits on them, they trap the rider in place and refuse to let them off. They prey on the careless curiosity of travelers.