Mention the power of a human soul, and work from there

Monsters are just another species, but relationships with humanity... are tense.

Just throw it RIGHT into the story! (Not reccommended.)

Humanity exhibits powerful magic learned from those whose very bodies are magical in essence.

One of the important humans was directly responsible for inciting fear against monsters.

As long as you keep ponies in the focus of a gripping story, I really don't care.