Elementalist

Prerequisites: The ability to cast spell

You have an affinity towards a certain element. Select one of the following - acid, cold, fire, lightning, or thunder.
Whenever you cast a spell of one of those damage types, you can replace it with the damage type you selected when you took this feat.
Additionally, whenever you take damage of the selected damage type, you can reduce that damage by your proficiency bonus. If this would reduce the damage taken to 0, you instead take 1.