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.
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.
A living halloween mask, one of several created by a scientist.
Ascended Extra: In 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 its creator and turning Steve into his minion for the sake of getting to Carly Beth and possessing her again.
Worthy Opponent: As of "Scream of the Haunted Mask", it seems to regard Carly-Beth as its favorite host.
Once a normal young girl staying at "Camp Cold Lake", Della grew tired of the constant safety rules and became homesick. While trying to escape through the forest, she was killed by a rattlesnake, and now her lonely spirit roams the camp, desperate for a buddy to take her to the afterlife.