[@TheDarkTemplar] Work off existing lore. Define an influence - slavic, middle-eastern, anglo-saxon, german - any type of mythos, and create monsters based off them. For example, the world of the witcher is based off Slavic folklore.

You can create an Aglo-Saxon version of it with druids, trolls, hobgoblin, wyvern and will-o-the-wisp. 
https://en.wikipedia.org/wiki/English_folklore#Folklore_found_throughout_much_of_England
You could also make beasts off the Arabian myths, like Djinns, Nasnas, Ghouls and Ifrits.
https://en.wikipedia.org/wiki/Arabian_mythology

This can help: http://monster.wikia.com/wiki/Monster_Wiki .