Due to various circumstances, you have become endowed with the primordial might of storming thunder. Explain the origin of your newly awakened affinity; whether it is a divine blessing, the power of a bloodline, a strange coincidence, a deal with the (proverbial) devil, or some other fifth thing. Is it something you wanted? Did you have to sacrifice something to obtain this power? Has this elemental endowment brought about changes to your appearance or personality? If the source of your endowment isn't from the Elemental Planes, simply change the relevant narrative details to suit your character.

Anytime a feature of this martial archetype would push a creature any distance, it is pushed 5 feet less for each size class above your own.

Your save DC for this subclass is 8 + your Constitution modifier + your proficiency bonus.

Elemental Physique

3rd level martial archetype feature.

Divination reveals your creature type to be both Elemental and Humanoid and you are fluent in Auran. You gain resistance to thunder damage. You are immune to conditions or effects which would cause you to become deafened or incapacitated by mundane or magical loud sounds, thunder, or similar 'sonic' effects.

Thundering Steps

3rd level martial archetype feature.

Your movement speed is increased by 10 feet and you can dash and disengage as a bonus action. When you use these bonus actions, you create a loud boom that is audible up to 300 feet away.

Roaring Strikes

3rd level martial archetype feature.

Your attacks can count as thunder damage in addition to the normal damage type. Thunder damage caused by you ignores resistance to thunder damage and you can treat any 1 on a damage die as a 2 when rolling for thunder damage. Attacks imbued with thunder are very loud.

When you roll a thunder imbued critical hit, that hit creates a roaring boom that can be heard beyond 600 feet. The target must succeed on a Strength saving throw or be pushed 5 feet back and be knocked prone.

Endowment of Thunder Advancement Options

You can choose two of the following options at 7th level. You can choose one option at 10th and 15th levels.

Child of the Storm

Windstorms are like home to you. Rather than simply ignoring the negative effects of extreme winds, you can intuitively follow the storm's flow. Within strong wind, you have advantage on Wisdom (Perception) checks, Dexterity saving throws, ranged attack rolls, and initiative. In addition, you always have advantage on saving throws made to resist effects that rely on strong wind, such as a tornado or an air elemental's whirlwind.

Concussive Barrage

If you consecutively hit a creature with two or more attacks dealing thunder damage in the same turn, that creature must succeed on a Constitution saving throw or become concussed until the start of your next turn. A concussed creature cannot concentrate on spells and it suffers a –1d4 on any rolls that rely on Dexterity, Wisdom, or Intelligence.

Explosion

Once per short rest, you can use an action to emit a devastating Explosion that sweeps away everything within a 25 foot radius, centered on yourself. Each creature within this radius is deafened until the start of your next turn and must make a Strength saving throw. On a failed save, a creature takes 6d8 + your Constitution modifier of thunder damage, is pushed 10 feet back, and is knocked prone. On a successful save, a creature takes half as much damage and is pushed 5 feet back. You can control the explosion's radius to be smaller than its maximum, to a minimum of 5 feet.

The radius and damage of this ability increase at certain levels. At 10th level (30 ft., 8d8), 15th level (35 ft., 10d8) and 18th level (40 ft., 12d8).

Overwhelming Charge

You explode toward a creature with enormous force, making a melee attack accompanied by a roaring boom. Once per turn, if you move at least 20 feet straight toward a target and then hit it with a melee attack on the same turn, the target takes an extra 1d8 thunder damage and must succeed on a Strength saving throw or be pushed 5 feet back and be knocked prone. This ability can be used a number of times per long rest equal to your proficiency bonus.

The damage and distance pushed for this ability both increase at higher levels. At 10th level (2d8, 10 ft.), 15th level (3d8, 15 ft.), and 18th level (4d8, 20 ft.).

Shockwave

You can add your proficiency bonus to any thunder damage rolls you make against small or tiny creatures, swarm creatures, and creatures made of solid material such as stone, crystal, metal, etc. When you hit a small, tiny, or swarm creature with a thunder effect that would cause them to be pushed or thrown back, they are pushed an additional 5 feet.

Thundercloud Steps

While you are dashing, you can use a controlled shockwave to propel yourself through the air in a straight line for 15 feet. You can continue this movement while in mid-air, moving in any direction in 15-foot-segments and not exceeding your movement for this turn. While you are in the air, you have disadvantage on ranged attacks rolls. If you are still in the air at the end of your turn, you fall to the ground.

Whenever you fall 10 or more feet, you can use a reaction to negate the fall distance by a number of feet equal to half your movement speed.

Thunderous Palms

When you wield no weapon and carry no shield, your unarmed attacks have a +1 bonus to attack and damage rolls and a base damage of 2d6 + your Strength modifier. While unarmed, you can shove as a bonus action and you count as one size larger when determining the size of creature you can shove.

The bonus changes at 10th level (+2) and 15th level (+3). The base damage die increases at 18th level (2d8).

Thunderstrike

Three times per short rest, you can hurl the full force of your thundering might into an oppressive Thunderstrike. As an action, make a single attack accompanied by a brain-hemorrhaging boom. Hit or miss, the target creature and each creature within 30 feet of you is deafened until the start of your next turn. On a hit, the target creature must make a Constitution saving throw. On a failed save, it takes an additional 4d8 thunder damage, is pushed 10 feet back, and is knocked unconscious until the start of its next turn or until it takes damage. On a successful save, it takes half as much damage and is pushed back 5 feet.

The damage increases at 10th level (5d8), 15th level (6d8) and 18th level (8d8).

War Cry

You can release three types of thunderous war cries.

Challenging War Cry. Twice per short rest as a bonus action, you can bellow out a furious shout infused with primordial might. Each enemy creature that can hear you must succeed on a Charisma saving throw or become either provoked to attack you or frightened of you for 1 minute. The DM decides which is appropriate and can have a creature ignore this saving throw to be willingly provoked.

Rallying War Cry. Once per short rest as an action, you can imbue your voice with the vigor of a thunderstorm. Each friendly creature within 60 feet of you that can hear you has its movement increased by 10 feet for 1 minute and gains advantage on the first roll it makes before the start of your next turn. If a friendly creature within range that can hear you is currently affected by illusions or enchantments, it can reattempt the saving throw to throw off those effects. This counts as the first roll it makes before the start of your next turn.

Thundering War Cry. Once per short rest as an action, you can produce a thunderous roar which forces creatures within a 30 foot cone to become deafened until the start of your next turn. Each creature must then make a Constitution saving throw. On a failed save, a creature takes 3d8 thunder damage and becomes concussed until the start of its next turn. A concussed creature cannot concentrate on spells and it suffers a –1d4 on any rolls relying on Dexterity, Wisdom, or Intelligence. On a successful save, a creature takes half as much damage and is not concussed. The damage of this ability increases at certain levels.

Thundering Surge

10th level martial archetype feature. Choose one option from the Endowment of Thunder Advancement Options.

You can enhance your action surge. During action surge, your movement speed increases by 15 feet and each time you hit a creature with a thunder-imbued attack, its movement is reduced by 10 feet until the end of its next turn.

Your Thundering Steps increases your base movement by 10 feet (20 feet).

Enduring Storm

15th level martial archetype feature. Choose one option from the Endowment of Thunder Advancement Options.

You gain immunity to thunder damage and your hit point maximum is increased by 1 per character level.

Thunder God

18th level martial archetype feature.

Divination reveals your creature type to be only Elemental. Your maximum score for Strength and Constitution are both increased by 2. This does not increase your current scores for those abilities.