Soul Warden

Soul Wardens are able to harness the souls of enemies that they've just killed and infuse it into their blades or use their souls for spellcasting. All spells, no matter the original spell, will always do necrotic damage, as it is harnessing the souls of the recently departed. At later levels, Soul Wardens can consume the souls rather than casting spells or infusing their blade, allowing themselves to heal from the previous battle.

Rotting Blades

With every kill, it gets easier. The Soul Wardens have the ability to coat their blade with the soul of their most recent victim. When you participate in combat and your target dies, you can use a bonus action to coat your blade with their soul. For the next two turns, the weapon you coated now does an additional 1d6 necrotic damage. If another target dies while Rotting Blades is active, the duration is doubled. At 9th level, the necrotic damage now deals an additional 1d8 damage. At 17th level, the necrotic damage now deals an additional 1d12.

Soul Magic

At 3rd level, your control over souls grow and let you cast magic. If a target dies near you, you can use a bonus action to grant yourself one cantrip and one spell for two turns. These are treated as level one cantrips and level one spells and all damage that is dealt with this spell is converted to necrotic damage. At level 9, the spells are upgraded to 2nd level cantrips/spells.

The Nutrients of The Soul

At 9th level, you discover that the soul doesn't have to be used in destructive ways. When a target dies near you, you can use a bonus action to collect the soul to use Nutrients of The Soul. Using Nutrients of The Soul lets you heal for 3d4 hit points. You can also target an ally with this ability, but can only heal them for 2d4 hit points.

Soul Rip

At 13th level, you crave the souls in living targets and take action. You gain the spell Soul Rip. You can target one creature and attempt to rip their soul of their body, making them roll a constitution saving throw. If it fails, they are dealt 4d10 necrotic damage. If succeeded, they are dealt 2d10 necrotic damage. 

Ghost Walk

At 13th level, you can phase partially into the realm of the dead, becoming like a ghost. As a bonus action, you assume a spectral form. While in this form, you have a flying speed of 10 feet, you can hover, and attack rolls have disadvantage against you. You can also move through creatures and objects as if they were difficult terrain, but you take 1d10 force damage if you end your turn inside a creature or an object.

You stay in this form for 10 minutes or until you end it as a bonus action. To use this feature again, you must finish a long rest or destroy one of your soul trinkets as part of the bonus action you use to activate Ghost Walk.

Tokens Of The Departed

At 17th level, Soul Wardens are able to manifest souls into trinkets in order to reserve them for later. Soul Wardens can now take a bonus action when someone dies near them to make them into a token (appearance is determined by the player as long as it is small) that contains a soul. Souls can be used on a bonus action for the other spells related the the Soul Warden or even sold to merchants. The amount of gold you get from a soul trinket is dependent on the merchant and the soul that is contained in the trinket.