The Bog Unicorn is a horse that came back from the dead with a sword stuck through its head. It is a mount that can be used by the Inquisitor. The Bog Unicorn is available as part of the DLC that comes with Dragon Age: Inquisition Deluxe Edition and Dragon Age: Inquisition Inquisitor's Edition.
Official description Edit
Once belonging to an evil marauder, this unique mount has returned to inspire fear into those who would oppose you.