Elemental Fighter (5e Feat)
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You have learned to harbor an element with yourself and unleash it at will. You gain the following benefits:
•When you gain this feat, choose one of the following damage types: acid, cold, fire, lightning, or thunder.
•You gain resistance to the selected damage type.
•When you deal damage with a weapon attack or an unarmed attack you may expend one of your Hit Dice to deal extra damage of the selected damage type.