Shape shifters One form of limitations could be that the shapeshifter needs an animal pelt, such as the selkie skin, or forms of the werecreature myths. In some werecreature myths, the person could only shift with the removal of clothes, and only become human again by putting on their clothes again.
This one is just bloody terrifying full stop. Monsters hiding in closets or under the bed are a thing of nightmares for most kids. A skeletal type monster with crazy hair would definitely terrify me as child.
Digital Concept Artwork - 'Vs The Lich' by Rachel George