The power of one or two elements literally courses through your veins. Choose one of the following benefits when you select this species at character creation; you can use the chosen benefit a number of times equal to your Proficiency Bonus, but not more than once per turn. You regain all expended uses when you finish a Long Rest:

Fire’s Burn (Fire). When you hit a target with an attack roll and deal damage to it, you can also deal 1d10 Fire damage to that target.

Smoke Step (Fire and Air): As a Bonus Action, you create a 10-foot Emanation of thick smoke centered on you until the end of your next turn. Everything inside the Emanation is Heavily Obscured.

Aerial Jaunt (Air). As a Bonus Action, you gain a Fly Speed equal to your Speed and can hover until the end of your turn.

Frost’s Chill (Air and Water). When you hit a target with an attack roll and deal damage to it, you can also deal 1d6 Cold damage to that target and reduce its Speed by 10 feet until the start of your next turn.

River's Run (Water). You always have a Swim Speed equal to your Speed. As a Bonus Action, you can end every effect on yourself giving you the Grappled, Prone or Restrained conditions, and you can move through a space as narrow as 1 inch without expending extra movement until the end of your next turn. 

Mud Mask (Water and Earth): You can cast Disguise Self without a spell slot, using Constitution as your spellcasting ability.

Stone’s Endurance (Earth). When you take damage, you can take a Reaction to roll 1d12. Add your Constitution modifier to the number rolled and reduce the damage by that total.

Lava Lick (Earth and Fire). When you take damage from a creature within 60 feet of you, you can take a Reaction to deal 1d8 Fire damage to that creature.

Choose one or two of the following damage types: Acid, Cold, Fire, Thunder or Lightning. If you choose one, then you have Immunity to that damage type. If you choose two, then you have Resistance against both of those damage types.