<your character> discovered the ability of abyss walking; earning you the title: <your name> the Abysswalker. This allowed him to enter The Abyss, the home of the Darkwraiths and the Four Kings themselves. At some unspecified time in the past, when you were attacked and defeated by the Abyss and Manus, Father of the Abyss.
<your character> sacrificed his great shield to protect his loyal companion, a young Sif (great grey wolf), from the myriad Humanity Sprites that littered the deepest reaches of Oolacile. Oolacile was a kingdom that existed in Lordran.

With his left arm shattered following his confrontation with Manus, he had no use for the shield and chose to wield his greatsword in his one good hand. With time, <your character> became fully corrupted by the Abyss (though, in hunting the corrupted denizens of the abyss and the abyssal creatures, it is clear he didn't wholly forget his mission).

after making a deal with one of the four kings of the abyss, <your character> is granted full control/power over the corporation that's within him (the abyssal corporation from earlier), harnessing the powers of the abyss. using those powers to defeat Manus, Father of the Abyss. (after that you can choose how the story goes whether you defeat him or lose again)

inspired from Artorias the AbyssWalker (dark souls)

 

Great, At A Great Price

(this is optional)
your right arm gains incredible strength, but your left arm is forever shattered, no magic can heal it, or help it recover (your left arm is weak). 

you can wield (heavy, two-handed) & (Versatile) weapons with one hand effectively (the right hand).

you can expend one abyssal reserve to coat your left hand with shadows at will. empowering your arm from the inside and outside. it stays coated Until you dismiss it, or fall unconscious.
when your left arm is coated, your "Unarmed Strike" is considered a weapon that deals 1d4 + "STR modifier"  necrotic damage.
at the 15th level 1d6+"STR modifier"
your left arm can't carry any weapon or shields, nor use two-handed ranged weapons such as bows. (heavy crossbows can be used with your right arm)

active

activate all the features

Inactive

deactivate the feature

Children of Darkness

At 3rd level, you no longer have your eyes hindered by the presence of darkness. You can see through normal darkness, up to a range of 120 feet. and magical darkness at the 10th level.

 you learn abyssal.

all shadows whisper to you the true intention or thought of the projector. roll an insight check contested by a deception check.
if the caster of the shadow is a creature and is sleeping, you can talk with its shadow.
(you don't need to share a known language)

Abyssal reserves

you have a pool of darkness inside you called (Abyssal reserves or Abyssal Levels) you can pull from it to enhance your abilities or to create shadows from your body, that you command.
you use the inner abyssal energy to use one feature of Abyssal Might. Abyssal reserves are equal to half your fighter level rounded up. and you regain all expanded when you finish a short/long rest.

expended one level to activate one Abyssal Might feature.

Abyssal Might

at 3rd level, you can use your inner Abyssal reserves of vitality to draw from the power of darkness, unleashing it upon your enemies. (one of the following )

Abyssal Power. As a bonus action, you and a weapon you wield became coated by an aura of shadows that lasts for a minute, which gives you a number of temporary hit points equal to half your fighter level. When you hit a creature with that weapon, deal an extra 1d4 necrotic damage. the weapon stays coated for the duration. 
(this ability can not be activated again until a minute passes)
at the 12th level 2d4 necrotic damage.

Abyssal Wisper. As a bonus action, a weapon you wield became coated by a faint aura of shadows that lasts for a minute, When you hit a creature with that weapon, deal an extra 1d6 psychic damage. the weapon stays coated until it departs your hand.
at the 12th level 2d6 psychic damage.

Abyss Sludge. As an action, you send forth a thick fog of shadows in a 20-foot cone casted from your left-hand palm.
Creatures in the area must succeed on a Constitution saving throw (DC 8 + your proficiency bonus + your Constitution modifier) on save half damage otherwise; take 1d8 necrotic damage.
The damage increases to 2d8 at the 7th level,   3d8 at the 10th level,   and 5d8 at the 15th level.

Shadow Leap. As a bonus action, you can be carried by the shadows you command, up to 30 feet in any direction. This movement doesn't provoke opportunity attacks, and you fall if you end your turn in the air.

Shadow servant. As an action, you expend 3 Abyssal reserves, to summon from your shadow a shadow servant, this servant can't go 120 feet away from you and you can control him verbally during your turn. (unlocks at level 10)

"all abilities other than Shadow servant, consume 1 Abyssal reserve"

abyssal power and whisper can't be activated on the same weapon.

 you unlock two when reaching 3rd level of your choice, and one more on the following levels 7,10,15.

Abyss Sludge

Abyss Sludge. As an action, you send forth a thick fog of shadows in a 20-foot cone casted from your left-hand palm.
Creatures in the area must succeed on a Constitution saving throw (DC 8 + your proficiency bonus + your Constitution modifier) on save half damage otherwise; take 1d8 necrotic damage.
The damage increases to 2d8 at the 7th level,   3d8 at the 10th level,   and 5d8 at the 15th level.

save DC = (8 + proficiency bonus + Constitution modifier)

Abyssal Powers

Abyssal Power. As a bonus action, you and a weapon you wield became coated by an aura of shadows that lasts for a minute, which gives you a number of temporary hit points equal to half your fighter level (rounded down). When you hit a creature with that weapon, deal an extra 1d4 necrotic damage. the weapon stays coated for the duration. 
(this ability can not be activated again until a minute passes)
at the 12th level 2d4 necrotic damage.

Abyssal Wisper

Abyssal Wisper. As a bonus action, a weapon you wield became coated by a faint aura of shadows that lasts for a minute, When you hit a creature with that weapon, deal an extra 1d6 psychic damage. the weapon stays coated until it departs your hand.
at the 12th level 2d6 psychic damage.

Shadow Leap

Shadow Leap. As a bonus action, you can be carried by the shadows you command, up to 30 feet in any direction. This movement doesn't provoke opportunity attacks, and you fall if you end your turn in the air.

Shadow servant

Shadow servant. As an action, you expend 3 Abyssal reserves, to summon from your shadow a shadow servant, this servant can't go 120 feet away from you and you can control him verbally during your turn. (unlocks at level 10)

Shadow Step

At the 7th level, you can use natural shadows as gates through to the abyss, allowing you to teleport from shadow to shadow. When you are in dim light or darkness, as a bonus action you can teleport up to 60 feet to an unoccupied space you can see that is also in dim light or darkness. You then have an advantage on the first melee attack you make before the end of the turn.

you can use it a number of times = to your proficiency.  regain all expended on long rest.

Leap Attack

At the 7th level, as a reaction when you are targeted by a creature within 30 feet, you can jump into the air, adding half your Proficiency (rounded down) to your AC against the attack (potentially making the attack miss), and land within 15 feet of your original spot, without provoking opportunities.

You can then make an attack with your unarmed strike; if a creature is within reach.

you can use this feature up to your Proficiency modifier. regain all expended after a long rest.

Corrupted Nature

At the 10th level, your body has forever been tainted by darkness. You no longer need to eat, drink or breathe, and you no longer age.

your mind becomes fully corrupted and shielded by the abyss, you gain resistance to necrotic and psychic damage.

to long rest, you meditate: at night, or in the dark, or at a bonfire for 4 hours straight.

The Last Scream

At the 15th level, when your HP drops to 1/3 of your maximum HP, you scream one Last scream, calling the Abyss within you. and your body starts summoning dark/shadowy souls. every hostile who can hear/see you. must make a Wisdom save save DC = (8 + proficiency bonus + Constitution modifier), on failer is frightened. and takes 3d8 psychic damage. on success half damage.
you gain for the next 10 minutes resistance to slashing, piercing, bludging, force, and +3 to AC.
this feature can be used once per dawn.

The last Scream active

use this, when your HP drops below 1/3 of your maximum HP
this will activate all the benefits
after 1-minute passes return it back to inactive

The last Scream inactive

use this until your HP drops to 1/3 of your maximum HP
this will keep everything inactive

Abyssal Wrath

When you reach the 18th level, you can use your bonus action to wreath your body and the area around you in abyssal essence. abyssal essence is a supernatural substance, it is the true embodiment of the darkness.
For the next 10 minutes, you surround yourself with abyssal essence (20 feet radius sphere) that is dense on the core and lighter on the outer 10 feet, and gain the following benefits:

- You become immune to necrotic, psychic damage, and to the poisoned condition. also, gain resistance to poison damage.
- Dim light within 10 feet of you becomes darkness that no source of light can shine in it, and bright light 10 feet farther becomes dim light.
- as a reaction. your shadows lash at the attacker if he is within 15 feet. dealing 4d8 necrotic damage.
- any attack within 10 feet of you is at a disadvantage.

Once you use this feature, you can't use it again until you finish a long rest. You regain one use of this feature when you use your Second Wind.

Abyssal Wrath active

use this when you use the feature

all benefits are on and available

Abyssal Wrath inactive

use this untill you use the feature

all benefits are off