Monsters

Monsters in Tir Eriad are varied in form, source, and relative intelligence and motivation. What some individuals may refer to as "monsters" may simply be creatures seeking to survive in the wilds of Tir Eriad. While a significant majority of Tir Eriad's non-human, non-Faen races are indigeonous to Tir Eriad, the Reckoning of the Tre'Luinn at the start of the First Age also drew a large number of non-native species and in some cases, warped them beyond what would be recognized in their original worlds. Furthermore, continued existence on Tir Eriad has caused some of these new species to become inured to a various elemental forces that exist in the world, and thus they have further warped over time, some to great detriment, some to great advantage as they all seek out their new ecological niche. 
As monsters have become infused with elemental forces, including light and shadow, they typically take on traits of those forces. For example, creatures that are infused with shadow eschew light, and can have a voracious appetite for living creatures around them. Those infused by light will give a visible glow at night, occasionally causing lost travelers to follow them, sometimes to their deaths. Most importantly to note, is that monsters on Tir Eriad are not evil or good (regardless of the opinion of the individuals that occasionally brush up against their territories) but are primarily driven by their desire to survive, territorial instinct, elemental bent, as well as (in terms of the more intelligent creatures) higher level motivations such as expansion or power that are not absent from human kingdoms as well.