Horned steed
Horned steed is an elemental of Lumen, a shape called out of the Welter in the form of a white steed with a single horn. A mage casts Summon horned steed, and it comes out of the light at a gallop.
It strikes first with raw power from its horn, then with its hooves, and it is fast. Its upkeep is paid in geld and mana; stop paying and it is dismissed.
Lumen cultivators tell a story about its temper. In the Age of the First Sealborn, a veteran struck out Wen Sarai of the Newcomer's Grace shortly after she arrived, and Daegred, the Sunward made the Newcomer's Grace, which shelters a newcomer until the Covenant first weighs their kingdom. The horned steed, they say, keeps that law in its own way. It will not let anyone ride it who has struck a newcomer.