Misdreavus is a dark bluish-green, ghost-like Pokémon. While it has no visible arms or legs, its lower half has several small appendages and resembles a ruffled dress. It has several round red gems around its neck, which are used to absorb fear and use it as nourishment. When defeated in the side series games, its body disappears, leaving only the gems around its neck behind. This implies that Misdreavus retreats into the gems when it has been severely weakened. It has long, flowing lilac-tipped "hair". Misdreavus's large, red eyes have yellow sclerae.
Misdreavus lives in caves. As a nocturnal Pokémon, it spends its days sleeping in darkness and its nights startling people with mischievous tricks. Since it loves watching frightened people, it is known to yank and bite at people's hair or sneak up on them and cry and shriek in a way a child would. In the anime, Misdreavus is shown to be able to use its "hair" to grasp objects and other Pokémon, as if it were hands. Flutter Mane shares a resemblance to Misdreavus. It was theorized to be a giant Misdreavus reborn as a pterosaur ghost.
In Misdreavus Misgivings, Morty's Misdreavus is one of his strongest battlers, being able to both exploit its own abilities and those of its opponents using non-damaging attacks like Spite. Having used it in the Gym Leaders' Tournament match (which ended in a draw due to it using Destiny Bond), he still keeps it in his team to this day.
Misdreavus' nocturnal habits of wailing to frighten people and its similarity in appearance to a disembodied head are shared by various mythological creatures. One of these is the nukekubi, which shares the similarities of nocturnal habits, flying about as a decapitated head, and wailing to increase its victims' fright. Another possible source of origin is the banshee, a female spirit from Irish mythology, known in modern media for its unearthly wailing and screaming. Its shape also resembles the Teru teru bōzu and the typical depiction of a ghost with a bedsheet. The red orbs look similar to a Japamala.
Its names in different languages referencing dreams also point to Mares as a possible inspiration.
Misdreavus may be a combination of mischievous and dream. It may also involve mistress, miscreant, dread, and dreary.
Muma may be derived from 夢魔 muma (nightmare; demon in a dream).