Species

Monster High, being a monster-themed franchise, features a huge cast consisting of many different types of monsters. And some humans to round it out, of which most fit the conventions of the horror genre. Below is the entirety of the cast listed by species, with those who are either unknown or unique to the franchise listed as "other".

Please keep two things in mind when reading:
 *  The monster history articles linked to are not necessarily fit for reading by a young audience. 
 * Characters are primarily grouped the way canon does it, even if canon would conflict with source conventions. Where canon is silent, source conventions are utilized.

Other
The following entries are characters that are the only one of their kind in the cast of Monster High or are species mentioned but devoid of characters to represent them.
 * Andy Beast (unknown)
 * Astranova (alien)
 * Batsy Claro (vampire bat)
 * D'eath (Grim reaper/Skeleton)
 * Eyera (eyeball head monster)
 * Gob (blob creature/unknown exactly)
 * Gooliope Jellington (unknown)
 * Headless Headmistress Bloodgood (headless horseman)
 * Irene Maiden (unknown)
 * Jackson Jekyll/Holt Hyde (Dr. Jekyll/Mr. Hyde/human/elemental)
 * Jane Boolittle (unknown)
 * Kala Mer'ri (cecaelia)
 * Short lunch lady (unknown)
 * Tall lunch lady (unknown)
 * Mouscedes King (rat king or "Rat Princess")
 * Music teacher (unknown)
 * Neighthan Rot(H) (unicorn/zombie)
 * Mr. Ogrethor (ogre)
 * Lothar (possibly ogre)
 * Perfect Guy (unknown)
 * Peri and Pearl Serpentine (hydra)
 * Posea Reef (sea goddess or unknown)
 * Raythe (unknown)
 * River Styxx (skeleton/grim reaper/ghost; not hybrid, special mix-oriented monster from being a grim reaper) (Not H)
 * Scarah Screams (banshee)
 * School photographer (unknown)
 * Slug girl (anthropomorphic slug monster)
 * Tiki (sapient Tiki statues)
 * Twyla (boogeyman/boogey monster)
 * Nerd boy (unknown)