Path of the Storm Herald (5A)

Typical barbarians harbor a fury that dwells within. Their rage grants them superior strength, durability, and speed. Barbarians who follow the Path of the Storm Herald learn instead to transform their rage into a mantle of primal magic that swirls around them. When in a fury, a barbarian of this path taps into nature to create powerful, magical effects.

Storm heralds are typically elite champions who train alongside druids, rangers, and others sworn to protect the natural realm. Other storm heralds hone their craft in elite lodges founded in regions wracked by storms, in the frozen reaches at the world’s end, or deep in the hottest deserts.

Source: Xanathar's Guide to Everything

Subclass Features

Storm Aura

When you select this path at 3rd level, you emanate a stormy, magical aura while you rage. The aura extends 10 feet from you in every direction, but not through total cover.

Your aura has an effect that activates that turns on when you enter your rage and has an effect that activates at the end of each of your turns until your rage ends. You can change which aura you emanate , and you can activate the effect again on each of your turns as a bonus action. Choose desert, sea, or tundra. Your aura's effect depends on that chosen environment, as detailed below. You can change your environment choice whenever you gain a level in this class.

If your aura's effects require a saving throw, the DC equals 8 + your proficiency bonus + your Constitution modifier.

Desert. When this effect is activated, all enemies other creatures in your aura take 2 fire damage each. The damage increases to equal your proficiency bonus. when you reach certain levels in this class, increasing to 3 at 5th level, 4 at 10th level, 5 at 15th level, and 6 at 20th level.

Sea. When this effect is activated, you can choose one other creature you can see in your aura. The target must make a Dexterity saving throw. The target takes 2d6 1d6 lightning damage on a failed save, or half as much damage on a successful one. The damage increases when you reach certain levels in this class, increasing to a number of d6 equal to your proficiency bonus. 2d6 at 10th level, 3d6 at 15th level, and 4d6 at 20th level.

Tundra. When this effect is activated, each creature of your choice in your aura gains 2 temporary hit points, as icy spirits inure it to suffering. The temporary hit points increase to equal your proficiency bonus. when you reach certain levels in this class, increasing to 3 at 5th level, 4 at 10th level, 5 at 15th level, and 6 at 20th level.

Storm Soul

At 6th level, the storm grants you benefits even when your aura isn't active. The benefits are based on the environment you chose for your Storm Aura when you last used it.

Desert. You gain resistance to fire damage, and you don’t suffer the effects of extreme heat, as described in the Dungeon Master's Guide. Moreover, as an action, you can touch a flammable object that isn't being worn or carried by anyone else and set it on fire.

Sea. You gain resistance to lightning damage, and you can breathe underwater. You also gain a swimming speed of 30 feet.

Tundra. You gain resistance to cold damage, and you don’t suffer the effects of extreme cold, as described in the Dungeon Master's Guide. Moreover, as an action, you can touch water and turn a 5-foot cube of it into ice, which melts after 1 day, unless the temperature is freezing in which case it lasts until thaw. minute. This action fails if a creature is in the cube.

Shielding Storm

At 10th level, you learn to use your mastery of the storm to protect others. Each creature of your choice has the damage resistance you gained from the Storm Soul feature while the creature is in your Storm Aura.

Raging Storm

At 14th level, the power of the storm you channel grows mightier, lashing out at your foes. The effect is based on the environment you chose for your Storm Aura you are using.

Desert. Immediately after a creature in your aura hits you with an attack, you can use your reaction to force that creature to make a Dexterity saving throw. On a failed save, the creature takes fire damage equal to your Barbarian level.

Sea. When you hit a creature in your aura with an attack, you can use your reaction to force that creature to make a Strength saving throw. On a failed save, the creature is knocked prone, as if struck by a wave. You can only affect a particular creature with this ability once per round on your turn.

Tundra. Whenever the effect of your Storm Aura is activated, At the end of each of your turns when your tundra Storm Aura is active, you can choose one creature you can see in the aura. That creature must succeed on a Strength saving throw, or its speed is reduced to 0 until the end of your next turn, as magical frost covers it.

Editor's Notes

Straight upgrades again, and also made to confirm to newer designs.

You now choose what aura to manifest each tome you use the ability, and it lasts for the entirety of your rage. This required some changes to the effects, as you no longer activate your auras. I choose to have all aura effects happen at the end of your turn.
You can use a bonus action to change what aura you use.
The damage the auras do is equal to your proficiency bonus. This is not a major change for a single-class barbarian but has a lot of effect on a multiclass character. I am considering simply removing this.
Storm Soul/Tundra now lasts an hour. This makes it actually useful. Also, I live in a sub-arctic country and am familiar with ice; 125 cubic feet of ice does not melt in one minute. Nor does snow.
Raging Storm/Sea no longer uses your reaction, but is limited to one creature/turn, on your own turn.