[quote=Assallya]
I'm confused. It sounds like the "mythicals" never engage in conflict? You make it sound like they're incredibly peaceful compared to humans. What about monsters that must feed to survive: vampires, redcaps, and the like? What about the Faerie Court of the Sluagh? What about Orcs who rarely get along with elves and dwarves?
[/quote]

Actually, yeah, I made the "mythicals" out to be extremely peaceful. It was meant to be that they did not know the meaning of war or killing for other reasons than to feed. With that said, there were vile beasts back then, too. Sure, sometimes they napped someone and ate them. Sure, sometimes someone napped one of them and ate them, but that was considered the way of the world. Sure, the one being napped would probably try to fight to not get eaten, but no one else would help, since they knew that once the beast had eaten, it would go away again.
So, onto the rest; if vampires were to exsist in the world, it wouldn't be till [i]after[/i] the humans came and messed with everything. First of, vampires, depending on which of the very large amount of myths you choose, are usually considered undead humans of a sort who drink blood from other humans to stay alive. Actually, in far most of the myths, they are human in some way and thus not a species of their own. This would make them a sub-race to humans, in my book.
Redcaps are a human thing, too. They are just too... folklore-y or story-to-scare-children-y to really work for a fantasy RP, IMO.
Faerie Court of the Sluagh (had to google this, honestly) is as far as I could find out something about some souls of sinners stranded as "ghosts" in the living plane. Now, not that ghosts would be impossible; there might be someone who wasn't quite reasy to die, who did anyways and decided to hold on, but, yeah... dunno what to say...

*deep breath*

All in all, I think I'll go with a more simple explanation; I imagine the creatures already living in the world when the humans arrive to be, well, more animal-like than the ones who live alongside the humans. Like, they evolved to fit into a human-ruled world. 
I don't know if that makes sense or answers the question, but I sure do hope so ^_^'