I personally am sticking with the tried and true just giving them a new mythos. The Great Source created three creatures she considered her children. Dragons, Unicorns and Phoenix. All creatures related to shape shifting evolved from the Dragons. Fae, Elves and Pixies come from the Unicorns along with Pegasus of course. Then from the Phoenix we get all things related to the earth. Nomes, Trolls, volcano monsters all come from this realm.

Then there is the Shadow clan which is a unique member of both the dragon and phoenix. The shadows cast by the flame of a dragon reawakening a Phoenix brought to life a shape shifting clan of shadows that prefer to live in the shadows rather than come out into the light. They can however appear to be very human and thus made great spies into the human world.

All of this is brought to the human world when an underhanded attempt to steal the throne from the rightful Fae Queen.

The human world of course has its own monsters, Skinwalkers, and vampires though those are names given to " the changed" by the church and the churches hunters.

Basically I gave the old monsters and mythical creatures a new life by making the origins something more believable.