"I don't think he can control that thing."
As a series which deals in paranormal entities, both malicious and not, expect Martin Mystery to have plenty of terrors logged in the Legendex.
- The Boogeyman, a swamp demon composed of maggots who abducted children it deemed naughty, dumping them in its home dimension and leaving them to die. Particularly creepy is the large amount of old, broken toys found by the team in said dimension.
- The Black Spirit from "The Creeping Slime": a featureless, broadly humanoid, virtually unstoppable mass of constantly dripping grey slime.
- Clifford from "Eternal Christmas". He was perfectly willing to kill Martin and Diana, plus two innocent motorists who accidentally got stuck in the snow globe world, by baking them into fruitcakes in order to preserve his "perfect Christmas". Also some of the creepy faces he pulls.
- The Applebyes from "Mystery of the Vanishing" come off as an unsettlingly perfect Nuclear Family from the 1960s despite being trapped in an alternate dimension for decades, they haven't aged a day since they vanished. This is because they made a Deal with the Devil to the dimensions master, the Babylonian dragon Zook. In exchange for giving them eternal youth and immortality, they lead victims into his dimension every few years to have their souls eaten by the dragon.
- Both "Haunting of the Blackwater" and "The House of Zombies" feature some pretty terrifying examples of Demonic Possession. The latter being an homage to Evil Dead! The former also crosses into Tear Jerker when we learn why the spirit of Philus Blackwater possessed his inn. After his partners betrayed him, he refused to leave the inn he held so dearly; even after the heat was shut off… he was found dead, frozen solid in his chair.
