Argoribbles are nightmares that take the forms of purple fog with menacing faces. They possess a sleeper to give them nightmares, but are most vulnerable to light, and The Dreamstone.
They are usually prevented from menacing The Sleeping World, though regularly a very small number can break past the stone's power. On rare cases Zordrak and the Urpneys have also succeeded in sending a full mass of them onto the Land Of Dreams, usually by negating the stone's power in some way. They can also be empowered to resist their usual weakness with certain dark entities such as The Nightmare Stone or the Moon Of Doom.
Argorribles, when not spreading nightmares, rest in the pit surrounding Zordrak's throne. They appear to be the very few life forms the evil overlord shows compassion towards, helping him bring fear and anguish to his enemies.
Argorribles take the form of purple mist contorted with visible limbs and a menacing face with teeth. In Horrible Argoribble, it is revealed that some can be a solidify form of a monster, in which with Zordrak using his Book of Evil Principles, made one gigantic. Though if light shines it, it shrinks, as an alternative of scaring normal Argoribbles away.
In Mike Jupp's original manuscripts, Argorribles morphed out of their mist form when spreading nightmares, taking the form of menacing monstrous looking creatures to terrify their hosts.