The Deathless Revamped

"There are many tales of tireless warriors on the battlefield that are rumored to have the fortitude of the undead. These warriors didn’t have a name at first, until more of their kind started appearing in various battlefields alongside War-loving Zealots, Undead, and other abominations of Undeath. Because of this and where these fighters appear from, they were given a singular name that represents them as a whole, and that name is 'The Deathless' as they are beyond death itself in their ways of fighting and combat. These fighters are not known for finesse, or being versatile in their fighting styles, but instead rely on pure vigor, vitality, endurance, and strength as the necrotic essence in their body allows them to push beyond normal limitations of the mortal races."

Endless Toil

Beginning at 3rd level, you have advantage on saving throws against disease and poison. In addition, you don’t need to sleep and magic can’t put you to sleep. You can finish a long rest in 4 hours. If you spend those hours in an inactive, motionless state, during which you retain consciousness.

Deathly Vigor

Also, at 3rd level, as a bonus action, you channel the resilient resolve of undeath into vigorous energy for 1 minute. For the duration, you gain the following benefits: 

• You gain resistance to poison and necrotic damage. 
• When you activate this feature and, as a bonus action on subsequent terms while the benefit lasts, you can expend and roll one Hit Die. You regain a number of hit points equal to the number rolled plus your constitution ability modifier.
• When you drop a creature to 0 hit points, you gain temporary hit points equal to your Constitution modifier + your fighter level (minimum of 1 temporary hit points).

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

One Foot in the Grave

At 7th level, you gain immunity to diseases and have advantage on all checks and saving throws against extreme environmental conditions and exhaustion. Also, when you are targeted by any effect, you can choose to count as an undead, rather than a humanoid, for the purposes of determining creature type.

Grim Spirit

Starting at 10th level, your connection to the beyond has further strengthened and bolstered your body. Your Deathly Vigor feature grants you these addition benefits

• You now gain immunity instead of resistance to necrotic and poisoned damage
• If you roll a 1 or 2 on the hit die as part of this feature, you can choose to reroll but must use the new roll
• When you drop a creature to 0 hit points, you may choose either yourself or an ally within 10 feet of you to receive the temporary hit points

In addition, you no longer require food, water, and breathing. You regain all of your hit die after a long rest.

Tireless Mastery

At 15th level, whenever initiative is rolled, you may activate your Deathly Vigor feature. Also, whenever initiative is rolled and if you do not have any remaining uses of Deathly Vigor remaining, you regain one use of it.

In addition, you age at a slower rate. For every 10 years that pass, your body ages only 1 year, and you are immune to being magically aged.

The Undying

At 18th level, you gain the following benefits: 

• When you roll initiative and have fewer than half your Hit die, you regain 1d6 hit die. 
•  If you are subjected to an effect that instantaneously kills you, that effect is negated instead. 
• Once per long rest, if you are dropped to 0 points, you regain one-third of your hit points and you may choose to activate your Deathly Vigor feature.