I recently read Shadow Slave and I believe that fits as a dark fantasy. There is also Mistborn and Vampire Hunter D.
To me, dark fantasies focus on the cruelty of life and that can be reflected in the story's world building and magic system.
-High Stakes: Humanity is on the brink of collapse, or most humans are at the mercy of a powerful oppressive force.
-A brutal power system. There is a price for power.
-Showing how people can abuse their powers in horrific ways.
-horror and dread.
Dark fantasy is like throwing characters in a terrible life and death situation and seeing how they react under the stress. Do they compromise their values, ect.