From publisher blurb:
Always be yourself. Unless you can be a Unicorn!
Don’t be the last unicorn to join the party. Level up as a unicorn and grow from a foal to a Large mare or stallion as you embrace your untamable immortal essence and impale your foes with your horn; slay lions and dragons; disappear, change shape, or enhance yourself with the magic of your alicorn.
Create the unicorn you want to play in the Pathfinder Roleplaying Game while avoiding the pit falls of vanity and pride inherent to the perfect, immortal, and utterly superior nature of unicorns. This product includes the new unicorn race the re’em, racial traits, alternate racial traits, the core class archetype (which works with 28 different classes), the unicorn sorcerous bloodline, the paragon racial class (where you level up as a unicorn), and unicorn only feats. All so, you can play unicorns alongside any other player character in any high fantasy campaign setting.