are the spirits of those who were slain during battle. Fomors look like normal characters with black skin and glowing eyes. Their names usually follow the pattern of "Fomor (Job)," for example, "Fomor Thief."
The Fomors in Dynamis are the corrupted souls of the "multi-national" strike force (the majority being San d'Orian) known as the Hydra Corps who were transported to the Shrouded Land of Dynamis along with the elite beastmen units -- the Forlorn Vanguard and Dark Kindred.
The Fomors of Tavnazian Archipelago, who are spirits of soldiers slain during the invasion of the Tavnazian Archipelago, do not aggro until you kill up to 5 Fomors. At that point, they will aggro to sound. You can reset this "Fomor Hate" by avenging their deaths from the invasion by killing the Orcs, Gigas, and Tauri found in Tavnazian Archipelago. To check Fomor Hate, talk to Resauchamet in Tavnazian Safehold.
The Fomors in the Near East are the souls of the fallen Ephramadian soldiers in the war between the Kingdom of Ephramad and the Empire of Aht Urhgan long ago. Unlike the Fomors of Tavnazia, they do not possess any type of "Fomor Hate." There are also Fomors in Arrapago Reef that are the souls of those who have fallen in the struggle for the Astral Candescence. They too do not possess any "Fomor Hate."
While Fomors and shadows are related in that they are both humanoid undead (and can both be called "dark stalkers"), and are typically undead as a result of their spite or some sort of dark ritual, they possess different special attacks and have different appearances. Their relatedness becomes apparent while doing particular quests, especially those of white mage quests, and in Dynamis - Beaucedine, where the Hydra can use the TP attacks of both Shadows and Fomors.