Hellhounds

Hellhounds are introduced towards the end of the first installment of the series, M.E.R.C.E., with the character Puff. Hellhounds were originally created by Israfel as a way to give her warrior souls physical form and allow them to train with her in the Underworld. They have a natural pack mentality and actively seek others to bond with, regardless of species. They are also known to grow to the size of large horses and age much more slowly than humans, taking close to a decade to age mentally and physically by a single year. It is rare, though not unheard of, for a Hellhound to break through the barriers that separate the planes of existence, however, when they do it is nearly impossible to return them to the Underworld against their will.

As a rule, Hellhounds are not allowed to take human shape, due to the same law that governs Israfel's appearance, but it is possible if they know how. Many Hellhounds that have broken this rule choose to do so after they have reached two hundred years of age in an effort to blend in with either the humans in the Mundane World or the humanoid creatures of the Other Side. Once a Hellhound has chosen to abandon their wolfish skin, they almost never go back to it out of fear of being discovered and dragged back to the Underworld by Hecate.