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Due to its nature, Rapio was the first, or what was at least known, to be proof of intellect among the Twenty Primal Demons.

Powers: Rapio the Thieving was a slithering creature, despite its size, and although its loyalty was faulty, this was due to its nature, as Rapio used the venom that dripped from its fangs and flowed from its tongue to rob Sunguards of themselves, as the excretion mutated those it came into contact with to smaller replicas of the Demon, with no control over their actions. Rapio also seemed to possess some form of ability to lower its size and change its form, in order to escape the assault of the Sunguard.

Defeat and Aftermath: Despite its cunning, Rapio was defeated rather easily after the Twenty dwindled, and Sunguards developed the ability to burn the Demon's venom before the ooze could transform them. And the shapeshifting ability of the creature proved it's downfall, for as it shrunk, it was crushed under parts of The Ravager, weakened enough to fall to the Sunguard. Rapio was forced by an incantation to a size smaller than its true form, and then, stripped of its protective plates, and trapped between multiple rings of rock. But where its tongue falls, a miasma is formed and a putrid spring of its venom flows, still keeping its metamorphic effects.