Feats

Boon of the Furious Storm

Prerequisite
Level 19+, Spellcasting or Pact Magic feature
Ability Score Increase
+1 Intelligence or Wisdom or Charisma (max 30)
Source
FRHoF

You gain the following benefits.

Eye of the Storm

You have Resistance to Lightning and Thunder damage. While you are Bloodied, you have Immunity to Lightning and Thunder damage.

Storm's Strength

Creatures have Disadvantage on saving throws against your spells that deal Lightning or Thunder damage.