Aspect of the Firebird

You take on the aspect of a firebird (Tome of Beasts, p. 201), including some physical attributes. A fiery mantle descends upon you, resembling feathery wings and an expansive tail. You gain immunity to fire and a flying speed of 60 feet. Any creatures within 5 feet of you gain immunity to natural, environmental cold.
As an action, you can emit a blast of light 5 feet wide and 50 feet long. All creatures in its path take 6d6 fire damage and are blinded for 1d4 rounds. A successful Dexterity saving throw reduces the damage by half and negates the blindness. Each time you use this feature of the spell, its duration is reduced by 1 hour. When you expend the last hour of the duration, the spell ends at the start of your next turn.