Chthonic Sentinel

You have learned to tread the line of life and death. Fighters of the Chthonic Sentinel are so intertwined with the underworld, they constantly find themselves at the gates of said world. They're able to manipulate the afterlife in such a way that they can keep fighting far beyond when they should have stopped. Chthonic Sentinel fighters have been welcomed into death as a member of the living and as such are guardians of both worlds, able to hop between the two with ease.

Grave Walker

When you reach 3rd level, you learn exactly how to tread between life and death. Whenever you are reduced to 0 hit points but not killed out right, you may choose to instead drop to 1 hit point, after which you may immediately make one weapon attack against a creature within your reach. This attack deals an additional 2d4 necrotic damage.

You may use this feature twice, after which you must complete a short or long rest.

The additional necrotic damage increases to 2d6 at 7th level, 2d8 at 10th level, 2d10 at 15th level and 2d12 at 18th level.

Guardian of Life and Death

Your knowledge of the forces of life and death allows you to aid others and yourself. You gain proficiency in Wisdom (Medicine) and when you attempt to stabilize a creature with this skill, you make that check with advantage.

Ashes to Ashes

At 7th level, you gain proficiency in one skill, tool or language of your choice, and each time you fall unconscious you may swap that proficiency with another skill, tool or language.

Dust to Dust

At 7th level you are able to return to the earth from which you came. When you take damage, you may use your reaction to sink under the ground. When you do so you cannot be targeted by opportunity attacks. You then resurface within 10 feet of where you were at the start of your next turn and the first attack you make after resurfacing before the start of your next turn is made with advantage.

You must be standing on solid ground that is made of earth, or a flooring that has a thickness of no more than 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood.

You may use this feature a number of times equal to your proficiency bonus after which you must complete a long rest.

Reaper's Scythe

You can harm yourself to empower your attacks. At 10 level, once on each of your turn's when you hit with a weapon attack, you may choose to reduce your current hit points by 2d8. When you do so your attack deals an additional 4d8 necrotic damage.

Ghostly Constitution

At 15th level your body flickers with a ghostly aura. When you use your Reaper's Scythe feature, you immediately gain a number of temporary hit points equal to the amount of hit points your Reaper's Scythe feature reduced your hit points by.

Undying Resolve

Being so tied to death has given you the ability to allow others to withstand what they typically couldn't. At 18th level, friendly creatures within 60 feet of you, including yourself, have advantage on death saving throws.

Additionally, weapon attacks you make as part of your Grave Walker feature score a critical hit on an 18-20 and you can make 2 attacks as part of that reaction instead of 1.