Viperidae

The Viperidae are viper-like creatures that can be summoned to other realms. They are fiercely protective of objects they choose to guard.

Appearance
They are described as large and deadly. They are tall creatures, well over six feet, and have two long hinged fangs like their snake namesake.

Kingdom of the Wicked
In the first book, a Viperidae was summoned to the basement of the cathedral in Paloma. It is unknown who summoned it, but the creature becomes fiercely protective of Vittoria's amulet, which it keeps in its nest.

The Viperidae there is disturbed by Emilia when she goes in search of her sister's amulet.

Abilities
According to Wrath, should a Viperidae choose to guard something, no denizen of the underworld can interfere. Their venom is extremely potent and deadly, and for the few magic antidotes that exist, there are high costs.