Elemental mastery

Prerequisite: The Elemental Adept feat

• When you cast a spell that deals acid, cold, fire, lightning, or thunder damage you can change the damage type to a damage type you have chosen from the Elemental Adept feat. 

• When a spell you cast that deals damage of the chosen type that targets a creature with immunity to said damage type, treat the immunity as resistance instead. immunity changed to resistance in this way is not effected by the Elemental adept feat that states ignore resistance. additionally when you cast a spell that deals damage of that type, you can choose to re-roll a number of damage die equal to you proficiency bonus.

• when you cast a spell that deals damage of the chosen type, and is unaffected by the first ability stated within this feat, you may choose to make any number of the targets of that spell have a +5 on the DC against the spell. if a target was given a +5 bonus and fails the DC, they take maximum damage instead of the amount you rolled.