Vanquisher

All fighters strive to survive battles, but vanquishers thrive when on the edge of death. The riskiest fighters often become vanquishers to utilize the thrill of battle to hit a little harder.

Dying Blows

When choosing this archetype at 3rd level, you can utilize the extra thrill of being on death's door to add a little punch to your attacks. While at 0 hit points you can add your proficiency bonus to your damage rolls. 

Last Stand

Beginning when you choose this archetype at 3rd level, you do not fall unconscious after falling to zero hit points. Other rules about death saving throws hold true. If you gain all successes then your frantic energy fails and you fall unconscious and stable. 

AntiDeath Provisions

Starting at 7th level, when you fall to 0 hit points, you need a fourth success or failure before falling stable or dying. Natural 1s are still 2 failures and natural 20s still bring you back to 1 hit point. Additionally, it is even more difficult for your enemies to kill you outright. Instead of requiring double your maximum health's amount of damage to be instantly killed, triple your health must be dealt.
This becomes 5 death saving throws at 10th level and 6 death saving throws at 15th level.

Death Saving Throw Improvement

Starting at 10th level, you can add your proficiency bonus to death saving throws. Additionally you regain one hit point on a natural 19 or 20.

Vanquishing Blow

Starting at 15th level, while you are at one or zero hit points, when attacking an enemy you gain temporary hit points equal to the damage dealt. Damage that overflows the enemy's health is not counted. If the damage reduces the enemy to zero hit points, the temporary hit points are doubled.

Tis But a Scratch

At 18th level, you have played hopscotch in your own grave to the extent that death itself is too tired of chasing after you. You stop having conventional hit points entirely. Exactly how this works is at your Dungeon Master's discretion. One suggestion is to give your limbs hit points. If your body is entirely destroyed you will become a ghost. True death can only be accomplished at will of the vanquisher or through the wish spell.