Netherim

You have learned to connect with the Netherrealm, a dank, infected plane that harbors near-eldritch abominations. Yet, somehow, you have harnessed the power that exudes from that plane, whether it be from a deal with a Champion of the Nether, or just by exploring. Either way, prolonged exposure to the Netherrealm has granted you abilities that involve the inclusion of such horrors, and your body acts as a vessel for such manifestations. 

Abyssal Script

Beginning at 3rd Level, when you adopt this archetype, your connection with the Netherrealm allows you to inscribe a series of runes onto a weapon of your choice. Once per day, you may spend 5 minutes carving a series of Abyssal characters onto a weapon of choice. The runes inscribed onto a weapon disappear after a long rest. While the runes are inscribed, that weapon gains the following benefits:

- The weapon cannot be dropped or removed by force. If it is, it simply returns to your hand.

- The weapon gains a +1 to attack and damage rolls made with it.

If your character does not know Abyssal, they learn it.

 

Nether Form

Beginning when you choose this archetype at 3rd level, you learn to draw on the power of the Netherrealm, a place parallel to the Nine Hells, and just as agonizing. As a bonus action on your turn, you may call upon the Nether, giving yourself a temporary boost to your power. You summon a spectral visage above your head, and your arms become shrouded in purple smoke.

For 1 minute, or until you dismiss this transformation, you gain the following benefits:

- Any attack made with a weapon inscribed with your "Abyssal Script" feature, or any unarmed strike,  deals an extra 1d6 necrotic damage.

- You gain advantage on Strength(Athletics) checks and on Strength Saving Throws.

- Your movement speed increases by 5 feet.

You may use this feature twice per day. You regain all expended uses upon long rest.

Abyssal Flash

 Your script gains additional bonuses. As a bonus action on your turn, you may cause the script on your blade to flash a pale green light in a 20-foot radius. Creatures of your choice within that area must make a Constitution saving throw (DC 8 + proficiency bonus + strength/dexterity) or take 2d8 necrotic damage, while you yourself heal for half the total damage dealt. You may use this feature a number of times equal to your proficiency bonus, and you regain all expended use on a long rest.

Improved Nether Transformation

At 10th Level, your transformation gains new bonuses. The visage above your head lowers onto your face like a mask, and purple tentacles emerge from the back of your head. You become plated in ornate gold pauldrons and a jagged spectral necklace adorns your neck. While in your Nether Form, you gain the following additional benefits:

- You gain temporary hit points upon transformation equal to twice your fighter level.

- The extra necrotic damage dealt with weapons inscribed with Abyssal Script and unarmed strikes increases by your proficiency bonus.

- You gain a bonus action bite attack that deals 1d6 + STR piercing damage and heals half the damage dealt.

- As a bonus action, you may let out a shout that invigorates you and your allies. Until the end of your next turn, you and your allies gain a +2 to attack rolls. You may use this feature only once per transformation.

Fury of the Nether King

At 15th Level, your runes become not just an anchor for power, but a mirror of the Netherrealm. You gain the following benefits:

- When a creature succeeds its saving throw on your "Abyssal Flash", it still takes half damage.

- Attacks made with weapons engraved with Abyssal Script deal additional psychic damage equal to your Strength/Dexterity modifier.

- You may now inscribe up to two weapons with Abyssal Script. 

- Alternatively, you may choose to inscribe armor with Abyssal. When this option is chosen, the armor gains a +1 to Armor Class, and any creature that targets you with a melee attack must make a Wisdom Saving throw or take 1d6 psychic damage.

Embodiment of the Nether King

At 18th Level, your devotion to the Nether has earned the interest of the King himself. While transforming, He has decided to aid you personally, granting the following bonuses:

- Your bite attack now deals an additional 1d6 psychic damage.

- Your size increases to Huge.

- Two of the tentacles coming from your head have gained enough strength to hold light items. They cannot hold shields, however.

- Your Strength Score increases to 24. This perk has no effect if your Strength Score would be higher without it.

- When wielding a heavy weapon, you may choose to wield it with one hand. When attacking this way, you may cleave up to three enemies within melee range. Make separate attack rolls for each target.

- Your rallying cry grants additional temporary hit points equal to half your Fighter level.

- When initially transforming, the amount of temporary hit points you gain increases to twice your fighter level.