[@Raylah] I dropped the ball here, so apologies on that! I generally play the plot-card close to my chest, but that just leads to more problems than ever, so I'll try being a bit more transparent!

[@TaroAndSelia] Basically, think of it this way: the further from major settlements you get, the less protection there is. Less patrols, less rounds of making sure the area is safe, and less guard posts along the way. So the world, or the kingdom if you want to talk smaller terms, has beasts everywhere, but their prevalence varies depending on WHERE you are. Near cities it'd be more common to find minor creatures, or more "natural" animals. 

If we're talking in the realm of like... Gryphons, just since you used that as an example, they're likely not hanging around cities or major towns - they'd be deemed a threat and killed pretty quickly. Humans (just using the broad term here for the sake of convenience) are the dominant species. 

As for the magic of the beasts, its safe to assume mythological creatures have SOME "magical" qualities to them. And there is a system in the world for that, since right now we have it that only Magi can use them. If you think about the criteria for what makes someone a Magi - outside of being born one, obviously, you can begin to guess at what species of beasts might have some type of magical ability.