Path of the Maelstrom Barbarian Subclass

Level 3. 

You gain the following while raging:

Thunder Smash - Once per turn when you reduce a creature to 0 HP or score a critical hit with a melee weapon attack, a shockwave erupts from you. All enemies within 9 meters take thunder damage equal to 1d4 + your Proficiency Bonus and are potentially knocked prone.

A Mighty Wind - Cast Gust of Wind at will as a bonus action without using a spell slot or requiring concentration.

Level 6.

You gain the following while raging:

Thunder Smash - Once per turn when you reduce a creature to 0 HP or score a critical hit with a melee weapon attack, a shockwave erupts from you. All enemies within 9 meters take thunder damage equal to 1d4 + your Proficiency Bonus and are potentially knocked prone.

A Mighty Wind - Cast Gust of Wind at will as a bonus action without using a spell slot or requiring concentration.

Walking Capacitor - Once per turn when a creature hits you with a melee attack, you gain six Lightning Charges, and the attacking creature gains two turns of Electrocuted.

You have resistance to Cold, Lightning, and Thunder Damage.

Level 10.

You gain the following while raging:

Thunder Smash - Once per turn when you reduce a creature to 0 HP or score a critical hit with a melee weapon attack, a shockwave erupts from you. All enemies within 9 meters take thunder damage equal to 1d4 + your Proficiency Bonus and are potentially knocked prone.

A Mighty Wind - Cast Gust of Wind at will as a bonus action without using a spell slot or requiring concentration.

Walking Capacitor - Once per turn when a creature hits you with a melee attack, you gain six Lightning Charges, and the attacking creature gains two turns of Electrocuted.

You have resistance to Cold, Lightning, and Thunder Damage.

Storm Lash - Once per turn when you hit a creature with a melee weapon attack, they take an additional 1d6 + your Proficiency Bonus lightning damage. Then, up to five arcs of lightning leap from the target to up to five other enemies within 9 meters, each taking 1d6 + your Proficiency Bonus lightning damage. These arcs automatically hit.