Due to various circumstances, you have manifested primordial energies originating from the Elemental Plane of Fire. 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? What physiological changes has this elemental endowment brought about? What are the physical characteristics of your fire? What color is it? Does it behave like normal fire? Etc.

If the source of your Endowment of Fire isn't from the Elemental Planes, simply alter the corresponding narrative details to suit your character.

Elemental Physique

3rd level martial archetype feature.

Divination reveals your creature type to be both Elemental and Humanoid. You have resistance to fire damage and you are fluent in Ignan.

Imbue Flames

3rd level martial archetype feature.

You can channel primordial flames through your body and into objects you touch. Your attacks can count as fire damage in addition to their normal damage type. Your fire damage ignores resistance to fire damage and you can treat any 1 on a damage die as a 2 when rolling fire damage. Fire you create ignites flammable objects that are not being worn or carried and sheds bright light for 15 feet and dim light for another 15 feet.

Using this feature, nonmagical weapons and ammunition made of flammable material inflict bonus fire damage equal to half your proficiency bonus, rounded down, and are destroyed at the end of the turn they were ignited.

Additionally, if you attack a creature and roll a critical hit, that creature catches fire (if it is possible to do so). Until it or another creature uses an action to douse the flames, it takes 1d10 fire damage at the start of each of its turns.

Endowment of Fire Advancement Options

You can choose one of the following options at 3rd, 7th, 10th, and 15th levels.

Eruption

7th level advancement option.

Once per short rest, you can use an action to emit a roaring eruption of fire that expands to fill a 25 foot radius sphere, centered on yourself. Each creature within the sphere must make a Constitution saving throw. On a failed save, a creature takes 5d10 + your Constitution modifier of fire damage and is staggered, having its speed reduced by 20 feet until the end of its next turn. On a successful save, a creature takes half as much damage and is not staggered.

The DC for this ability is equal to 8 + your Constitution modifier + your proficiency bonus.

The damage increases at 10th level (7d10), 15th level (9d10), and 18th level (11d10).

Fistful of Fire

You can wreathe your hands with dense, searing flames. Doing so allows you to use your fists as a melee weapon with a base damage of 3d4 + your Strength modifier fire damage and a reach of 5 feet. Alternatively, you can hurl the flames as a thrown weapon attack with an effective range of 100 feet and a max range of 300 feet. You are proficient in these attacks and both attacks count as normal unarmed or weapon attacks. Strength is your attack modifier for this ability.

This damage increases by 1d4 at 10th level (4d4).

Flaming Strike

You can use a bonus action to charge primordial fire into your next normal unarmed or weapon attack to produce a Flaming Strike that inflicts bonus fire damage in addition to the attack's normal damage on a hit. If you can make multiple attacks per action, Flaming Strike replaces one of them. This feature has a number of charges per short rest equal to three times your proficiency bonus. Each time you use this bonus action, you can expend a number of charges up to your proficiency bonus; inflicting 1d6 fire damage per charge.

Heated Body

A creature that touches you or hits you with a melee attack takes fire damage equal to your proficiency bonus. A creature takes this damage at the start of each of its turns it remains in contact with you. (e.g., if you are grappling.) This is in addition to any similar types of reactive fire damage offered by this martial archetype.

Igneous Armor

7th level advancement option.

Once per short rest, you can use an action to wreathe yourself in warding flames or semi-solid magma that will protect you from harm or return damage to your enemies. For 10 minutes, your AC is increased by 2 and you gain resistance to cold damage.

If a creature hits you with a melee attack while your Igneous Armor is active, you can use a reaction to scorch your attacker, inflicting 1d6 fire damage against them. Alternatively, when you take damage, you can use a reaction to fortify your igneous armor, reducing the damage you take by 1d6.

The damage and damage reduction increase at 15th level (2d6).

Lob Flame Glob

Using an attack action, you can toss a messy glob of liquid flame at a point within 60 feet of you, creating an incendiary splash that deals 2d6 + your Strength modifier of fire damage in a 10 foot cube. If you can make multiple attacks per action, Lob Flame Glob replaces one of them. A creature within the cube must make a Dexterity saving throw, taking full damage on a failed save and half as much on a success. This ability can be used a number of times per long rest equal to your proficiency bonus.

The DC for this ability is equal to 8 + your Strength modifier + your proficiency bonus.

This damage increases by 1d6 at 7th level (3d6), 10th level (4d6), 15th level (5d6), and 18th level (6d6).

Secondary Fires

When you miss a target with a fire imbued attack, you can use a reaction to deal fire damage equal to your proficiency bonus + your Dexterity modifier to a different target within 5 feet of the target you missed. The second target must be within range of your attack. You can use this ability a number of times per short rest equal to 1 + your Dexterity modifier (minimum of 1).

Soul Burning Flames

7th level advancement option. (Requirement: Intelligence score of 13 or higher)

Any fire damage caused by you can count as psychic damage in addition to its normal damage types.

You can use a bonus action to charge Soul Burning Flames into your next normal unarmed or weapon attack. If you can make multiple attacks per action, Soul Burning Flames replaces one of them. If the attack hits, a creature takes the attack's normal damage in addition to 1d12 + your Intelligence modifier of psychic/fire damage. A creature hit by this attack must then succeed on a Charisma saving throw or become frightened of you until the end of your next turn. This ability can be used a number of times per long rest equal to your proficiency bonus.

The DC for this ability is 8 + your Intelligence modifier + your proficiency bonus.

Stoking Barrage

If you hit the same creature with two or more consecutive unarmed or weapon attacks imbued with fire, the second hit and subsequent consecutive hits will inflict an additional 1d4 fire damage. This bonus damage does not stack and it ends if you miss an attack or use an action for something other than attacking that creature.

Boiling Blood

7th level martial archetype feature. Choose one option from the Endowment of Fire Advancement Options.

You gain immunity to fire damage, resistance to poison damage, and you have advantage on saving throws to resist magical and nonmagical diseases.

You can tolerate temperatures as low as −50 degrees Fahrenheit without any additional protection. If you wear heavy clothes, you can tolerate temperatures as low as −100 degrees Fahrenheit.

Blazing Surge

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

You gain the ability to enhance your action surge. When you activate action surge, each creature within 10 feet of you takes 2d6 fire damage. Until the start of your next turn, a creature that hits you with a melee attack or starts or ends its turn within 5 feet of you takes 2d6 fire damage.

Elemental Progression

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

Excluding fire elemental creatures, creatures with immunity to fire damage will instead take half damage from your fire.

Elemental Form

18th level martial archetype feature.

Once per long rest, you can use an action to transmute yourself into the purest primordial essence of flame. Your Elemental Form lasts until the end of your next turn and can be extended by expending two of your fighter hit dice for each additional round it remains active. Once your Elemental Form ends, you gain one level of exhaustion. If you use action surge while in this form, you gain one additional level of exhaustion after each time you do so; which takes effect after the Elemental Form ends.

While in your Elemental Form, you can directly manipulate the primordial energies of the elemental plane of fire, giving you access to the following benefits.

• You and everything you wear or carry becomes pure fire.
• You gain the size, speed, resistances, immunities, senses, and special traits of a fire elemental. Your hit points, ability scores, and proficiency bonus are not effected.
• Your normal unarmed and weapon attacks use the Touch attack action of the fire elemental, using your own modifiers.
• Upon activating your Elemental Form, any of your Endowment of Fire martial archetype features or abilities that have 0 uses remaining will regain 1 use.
• You can use an action to create a line of fire 60 feet long and 10 feet wide, extending from you in a direction you choose. Each creature in the line must make a Dexterity saving throw. A creature takes 6d10 fire damage on a failed save or half as much damage on a successful one. The DC for this ability is 8 + your Constitution modifier + your proficiency bonus.