Elemental Empower

When you hit with a weapon or spell attack, you may decide to add damage. Pick one of the following damage types: Acid, Cold, Fire, Lightning, Poison, or Thunder. You may add up to 4d6 of the chosen damage type. After damage is dealt, make a Constitution saving throw. The DC starts at 15 for 1d6 added, and it increases by 5 for every additional d6 of damage you add. If you succeed on the saving throw, there is no effect. If you fail, you also suffer the elemental damage you added to the attack and gain one level of exhaustion.