Crystalheart Avatar

You transform into a glowing avatar of crystal. While in this form: 

You gain 150 temporary hit points.

You shed bright light in a 30-foot radius, and allies within the light have advantage on saving throws against spells and magical effects.

As an action, you can release spend 30 of your temp hp to erupt a pulse of crystal energy a 20-foot radius pulse of crystal energy. Any chosen creatures in the radius must make a Dexterity saving throw, taking 5d8 radiant damage on a failed save or half as much on a success. 

This spell last for 1 minute or until concentration is broken.