Homebrew Ghost Man Species Details

Not quite living. Not quite Dead. Ghost Men were originally humans that bore a curse. This curse made originally made them prone to fits of madness, hallucinations, and and near feral violence, and would show up on one of the arms of the afflicted. Slowly making its way up and towards their heart. This is held back though sanctified chains. Though it is only a matter of time before they are taken over by demons.

However at some point during their life a specter would attach itself to them. This would tame and nearly erase the curse. The madness, hallucinations, and volatility are gone.

Ghost Men go through three stages of life.

Stage 1: Ghost
The physical appearance of the afflicted change. Their hair turns white, their skin pallid and cold to the touch, the irises become red, and the scaring from the curse extends fully to the heart. Either growing over the chest or the back but not both, and the scare itself becomes translucent only having physicality when the Ghost wants it to be for use. The next change is that the individual become sociopathic and cold towards other people. Loosing the ability to care past survival. Finally they cease to eat and drink, and when they sleep its only in a meditative like trance. Only falling fully unconscious when they become critically injured and need to heal.

Stage 2: Twined Specter
There is one physical changes to the body. The translucent arm with rematerialize and have and icy blue color to it. The Ghost Man begins to talk to itself from time to time, and act as though it is receiving answers. This is the beginning signs for stage 2. After a while a specter will sometimes form from the Ghost Man. It appears as grey fog/smoke. However when it comes to combat it will appear to defend the Ghost Man if they cannot defend themselves or provide them the opportunity to escape. When this happens the Specter will fully solidify and take on the form of a grey Skinned Oni with its face being covered in ritual seals found from the far eastern lands. This Specter is fully sentient and seems to genuinely want the best for the Ghost Man.

The Ghost man also seems to exhibit higher emotional awareness and ability. Now showcasing the ability to emote. Though its unknown if this  is genuine or just mimicry. The Ghost shows a higher adeptness for combat. Becoming faster and more precise with their attacks. Going for killing strokes and making attacks faster than the eye can see.
 Ghost Men spend a long time in this stage and unlike the first stage this one doesn't progress through time.

Stage 3: Rakshasa
In this stage the Ghost Man begins to show case a full range of emotions, but never seem to be taken by them. There hair color also changes back to their original color, and their arm begins to look crystalline in nature yet retains full range of motion. The Ghost Man also grows something akin to a second heart in the form of a demonic core. The curse scare now covers both their chest and back with a glowing crack going from their pectoral to their navel. The Specter now fully fights by their side in combat. Becoming more brutal in their strikes. Preferring to tear their opponents apart in contrast with the grace and speed of the Ghost. The seals have also disappeared leaving only their eyes covered. When fighting The Ghost Man Grows a crystalline horn on their forehead opposite to the side of their arm. Similarly the Specter has a grey horn on their head opposite from the Ghost's. In combat both Specter and Ghost seem to be able to change positions at will. With the Ghost Man capable of throwing a spectral blade that the Specter can spawn from. Now wielding its own blade.

Notes:
From stage 2 onward Ghost Men seem to follow a belief system similar to the Eight Fold path from Buddhism.
Ghost Men aren't only male. However the genitalia of both human sexes stop functioning upon entering the first stage.
Ghost Men seem to be ageless, and only look old if they looked like that prior to transforming. However there are no Children Ghost Men.
Ghost Men are very literal in their speech in the first and beginning portions of second stage. Almost not understanding metaphor and hyperbole.
Ghost Men seem to have a universal preference for keeping their altered arm uncovered at all times. Actively tearing or cutting sleeves off of clothing to do so.

Inspiration:
Dungeon Fighter Online: Slayer - Ghost Blade

As a Ghost Man, you have these special traits.

Trance

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 a trancelike meditation, during which you retain consciousness.

Skillful

You gain proficiency in one skill of your choice.

Keen Senses

You have proficiency in the Insight and Perception.

Savage Attacker

You’ve trained to deal particularly damaging strikes. Once per turn when you hit a target with a weapon, you can roll the weapon’s damage dice twice and use either roll against the target.