Summon: Regal Frostlion

Summon: Regal Frostlion is a skill that allows the summoning of a ride-able Regal Frostlion mount which runs at a movement speed of 280.

Source
The Regal Frostlion is learn-able via which was obtainable via digitally, or by retail pre–ordering the Collector's Edition of TERA: The Exiled Realm of Arborea. As such, this mount is no longer obtainable.