Stonehorn

The Stonehorn is less a beast than a moving piece of the mountains that bred it: a titanic creature of living rock and iron-hard hide, so massive and so slow to anger that lesser weapons shatter against it like rain on granite. Herds of them roam the highest, coldest peaks of the Mountains of Mourn, and to master one is the crowning boast of a Tyrant's whole life.

Ridden to war with a howdah lashed across its shoulders, a Stonehorn is a walking siege. It shrugs off cannon-fire and spear-hedge alike, then lowers its vast, stone-crowned skull and simply walks through whatever stands before it, goring, crushing, and grinding a battle-line to paste beneath feet the size of cottages. Nothing an ordinary army can bring to bear will stop it in time; the only mercy is that a Stonehorn is as hard to rouse as it is to kill, and by the time it is truly angry, the battle has generally already been lost for someone.