Elementalist

When you gain this feat, choose one of the following damage types: acid, cold, fire, lightning, thunder, radiant, or necrotic. You may take this feat multiple times, but you may not choose the same damage type more than two times.

• You gain resistance to the element of your choice.
• You may re-roll any 1 or 2 rolled on a damage die of your chosen element. If you reroll any dice, you must use the new roll, even if the new roll is a 1 or a 2.
• You can change the damage type of any spell that deals elemental damage to your chosen element.
• Spells that you cast with your chosen element ignore enemies’ resistance to that element.

• If you already have resistance to the chosen element, you gain immunity to that element.
• If you choose to take this feat multiple times and have chosen the same element once before, spells that you cast with your chosen element gain the following benefits:
• Spells now ignore enemies’ resistance and immunity to that element. 
• Enemies roll spell saving throws at disadvantage against spells of your chosen element unless those enemies benefit from immunity or resistance to your chosen element.
• You may add your spellcasting modifier to the damage roll of any spell of your chosen element.