Monster type: Terrestrial. Zappy is an anthropomorphic baby dragon or dinosaur-like creature with a bright yellow-orange body. She has large black eyes with sparkles and eyelashes, sharp teeth, small orange horns, and a vibrant magenta mohawk-style hair crest. She wears a fitted magenta short-sleeved t-shirt with the T.E.D.I. emblem on the chest, black shorts, and a control belt on her ankle. True to her name, Zappy is naturally lively and generally cheerful. She contrast strongly with Gloom's anxious caution and Nebulor's analytical confusion. While she is often cheerful, Zappy has a very short fuse. She is highly reactive, physically confrontational, and won't hesitate to punch first. Quirk: Electricity manipulation.

Monster type: Extraterrestrial. Nebulor is an anthropomorphic lime-green insect or alien creature with a rounded head, two prominent antennae, three large yellow eyes, and small buck teeth. He wears a blue checkered shirt over a white undershirt, paired with cuffed green pants and simple brown shoes, and a control belt on his left wrist. True to his quick, Nebulor is very intelligent, which makes him tend to show off his inventions. Nonetheless, he's still friendly and cares about his two friends, Zappy and Gloom, Unlike Zappy and Gloom, Nebulor does not possess any obvious supernatural powers. However, he is incredibly intelligent and resourceful. Quirk: None/Natural Intelligence.

Monster type: Dimensional. Gloom is a cyclops creature with a dark gray spherical body and a single large, striking yellow eye featuring a vertical black slit pupil and a small red triangular highlight, framed by a light blue-purple ring. He wears a black knitted beanie with ear-like spikes protruding from the sides and a small yellow tag with the T.E.D.I. crest. He has long, slender dark legs ending in oversized rounded feet, and a control belt on his left leg. Gloom is often deadpan about certain things. He is easily annoyed. Gloom has the ability to create black portals for teleportation, but he can only teleport to locations he has physically seen at least once in his life. He can also open portals to a dark dimension—an empty void where nothing is visible, and he himself becomes invisible. However, while his body is hidden in this dark dimension, his eye remains visible, which can reveal his location. Using these abilities appears to heavily drain his stamina. Additionally, Gloom can shapeshift: he can stretch his limbs to grab people, increase size to intimidate opponents, or transform into a small shadowy substance, allowing him to move quickly across walls/ceilings. Quirk: "Shadowy powers."