I just finished refining another class for 5e. The Demon Slayer class is a class that make every race fiend touched not just Tiefling. This class can of-course be used as a Tiefling as-well. To draw out this power one must have a good understanding of how it works a high intelligence if you will. I did think about using it use charisma for the save modifier however it just made more sense with me to use intelligence.
Demon Slayers much like the barbarian has a rage like feature. While in fiend trigger you get resistance to fire and poison, as well as gain an increasing amount of bonus to hit. This bonus to hit increases at certain levels.
Demon Slayers are also able to use Fiend Specific weapons, weapons which gain bonuses when in the hands of fiends. Like the Glaive from the bearded demons. As well as advantage against demon cursed items.

Demon Slayer.mod


Devil Arms: This archetype grants the user one of a few sentient weapons. You can choose or the DM can choose for you. These weapons will rank up as you level gaining more and more abilities. I put a little note in those abilities for the DM, if the dungeon master wants to work with the dm to come up with a personality for this weapon. Otherwise if y'all are just skipping it automatically gain the full benefits from the final archetype ability.

Gem Warrior: This archetype as you level you will gain different abilities based off what gems you choose as you level. You can gain the ability to fly, add cold damage to all your weapon attacks, even the ability to regenerate hit points. Depending on what you choose.

Epic Levels
The campaign i'm playing in is going go into epic levels, so i have written up extra class features for levels 21-30, this stuff however has yet to be tested and wont be tested for a while. I went with a different take on epic levels and gave a second archetype choice.

Nephilim: You focus more on the tanky aspect of the melee fighter, granting your more resistances, an increase to AC, and last the ability to absorb the damage your devil arm or gem warrior elemental damage type as temp hit points.

Darkkin: You focus more on the damage aspect of a melee fighter, granting you in combat teleporting, increase to your elemental damage type, a damage dealing aura, and an increase to damage based on half the bonus to hit you are getting.