From publisher blurb:
In the madness of World War II, a new power arises. Their Tesla-inspired technology creates fearsome and powerful new weapons on the battlefield. A backlash from a Tesla Arc opens a portal to the realm of Umbra, from which monsters of fairytale and legend return to Earth. Long ago, these creatures suffered being hunted and killed by humanity, and now they claim humans have captured their goddess. They are the aos sí, and they have returned for vengeance.
The Guardians of Umbra core book contains everything needed for players to create an aos sí from one of twelve races, each with their own unique abilities. With new Edges, Hindrances, spells, and gear, the player can take the fight to the corrupt Tesla Corps and reclaim Earth.
This book includes an all new Arcane Background, the Viscomancer. Collect parts from the bodies of your fallen foes to empower your magic. Enchant new relics to empower your adventures or steal the Tesla Tech weapons from your enemies and unleash a wave of electrical annihilation.