The archetypal Elemental Warrior hones their spiritual connection to the elements and the raw power associated with it. They channel this power into weapons made of pure elemental energy, and use this energy to destroy their foes. They are calm and focused in battle, sweeping through their foes with deadly confidence and focus. One would be wise not to aggravate such a warrior.

(A note on how this works in dnd beyond. Due to the complexity of the elemental weapons ability, you will have to add them to your sheet as custom actions. Also, for certain other abilities, the ability may show an option for something that is described as being based off of your current weapon. 

Elemental Weapons

The basis of your power comes from your ability to summon powerful weapons made of pure elemental power. When you gain this ability at level 3, choose 2 of the following damage types: Acid, Cold, Fire, Lightning, or Thunder. As an action, you can create a magical weapon made of pure elemental energy in an empty hand, choosing one of your chosen damage types when you do. Alternatively, you can summon two weapons of the same type with this action if you have two empty hands. These weapons are simple melee weapons with the light and finesse properties. On a hit, they deal 1d6 damage of the damage type chosen when creating the weapon. The weapon(s) lasts until you complete a long rest, create another elemental weapon of a different type, or dismiss your weapon(s) as a bonus action. If you use your bonus action to dismiss your weapon while you have two weapons active, you can dismiss either one or both of them with that bonus action. You can create a weapon in this way an amount of times per long rest equal to your wisdom modifier (minimum of 1).

At levels 5, 9, 13, and 17 you choose an additional damage type. Additionally, at level 5 the damage die that your weapon uses increases from a d6 to a d8. At level 13 this further increases to a d10.

 

Acid

Acid

Cold

Cold

Fire

Fire

Lightning

Lightning

Thunder

Thunder

 

Elemental Boon

At level 7, you are able to focus your inner elemental energy into your blade, allowing you to cast weak elemental spells through it. While holding your elemental weapon, you are able to cast a cantrip associated with that weapon's element. Your spellcasting modifier for these spells is Wisdom. You can use your elemental weapon as a spellcasting focus for these spells

Acid: Acid Splash

 

Cold: Frostbite

 

Fire: Fire Bolt

 

LIghtning: Lightning Lure

 

Thunder: Thunderclap

Acid

Acid Splash

Cold

Frostbite

Fire

Fire Bolt

Lightning

Lightning Lure

For whatever reason, ddb doesn't want to provide the spell as an option, so here is what it does:

You create a lash of lightning energy that strikes at one creature of your choice that you can see within range. The target must succeed on a Strength saving throw or be pulled up to 10 feet in a straight line toward you and then take 1d8 lightning damage if it is within 5 feet of you.

This spell’s damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).

Thunder

Thunderclap

Elemental Flare

Beginning at level 10, when you attack with your elemental weapon you become able to imbue it with increased amounts of energy for a moment. When you take the attack action, you can cause the elemental energy in your weapon to flare up. Any attacks made with your elemental weapon during that attack action roll two damage dice instead of the normal one for the weapon's damage (any other bonuses to its damage are not doubled).

Protection of the Elements

Your attunement to the elements grows stronger while your weapon is summoned, granting you protection to the type of damage that it embodies. While holding your elemental weapon, you have resistance to the damage type chosen when creating it.

Acid

Acid

Cold

Cold

Fire

Fire

Lightning

Lightning

Thunder

Thunder

Master of the Elements

Your mastery of the elements has grown so strong that you can create elemental weapons that embody multiple elements. Whenever you create an elemental weapon, you can choose two damage types instead of one. Your attacks with a weapon created in this way roll two damage dice instead of one, one for each of the elements of damage that the blade deals. 

For the purposes of Elemental Boon and Protection of the Elements, you are considered to be holding weapons of both elemental types while holding a weapon created in this way. When using Elemental Flare with a weapon created in this way, you can only roll two damage dice for one type of elemental damage instead of both