The Birdmen of Mount King

Concept: “Their king obsessed with making his mountains touch the very skies, he invented a new species of creature, obsessed with construction and architecture.”
Content: A race of labyrinth-building bird-people
Writing: Includes a description of their history and purpose alongside stats
Art/design: Appropriately creepy depictions of the subject and their lair
Usability: Easy to use, and its monster-summoning Special makes for difficult, escalating encounters