The Ashen Toll

You touch a creature that has been dead for no longer than 1 year and that died for any reason including old age. The creature is restored to life with all its hit points.

The creature is now undead and it does not need food, water, or air, and cannot die of old age or of exhaustion. It gains immunity to poison and disease, and all its missing body parts are restored, though wounds leave behind ugly scars. From now on, no wounds can be healed. Hitpoints can be restored, but if you lose an eye, for example, it is gone permanently.

Besides that, the resurrected person now gains a new attribute called humanity, which cannot be increased by any means. Humanity starts at a number corresponding to your wisdom ability score + the level of the spell + twice proficiency bonus. The undead loses 5 humanity every time it is killed, 1 every second year, 1 for every week spent in an unholy domain such as a region affected by a vampire's lair or one of the lower planes of existence, 1 for killing a humanoid creature, unless attacked by it. To identify that a person is under this curse, you must succeed on an arcana check. The DC is the undead's deception + their humanity.

Upon sinking to or below 15 humanity, the undead loses the routine of blinking and breathing, and its body is now only held together by the curse, therefore no new hair grows and it becomes pale as there is only old blood in its veins. The soul has been molded into a source of power, keeping the undead alive, while their personality leaks out of it, at the same rate as their humanity. Furthermore, they are cold as a corpse to touch and gains immunity to the exhaustion of extreme climates. 

Upon their humanity decreasing to 10, the undead start to wither, their skin becoming grey, wrinkled, and rotten and their eyes becoming dull. They now have disadvantage on all persuasion and entertainment checks. They also begin losing their will and personality gaining disadvantage on all non-intelligence saving throws.

Finally, when the undead's humanity comes below 5, it becomes so inhumane in appearance and personality that most civilizations will hunt them down. It only takes a DC 5 arcana check to figure out that this individual is a near mindless undead. They begin suffering from major amnesia and paranoia, being permanently frightened by sunlight and all other creatures good or evil unless the cursed know the creatures as friends. The undead is permanently charmed by those individuals. 

When an undead loses all its humanity, it becomes mad and the DM gains control of the character if they have not already. The type of undead the creature becomes depends on its might. If it is CR/level 5 or below it becomes a zombie or skeleton, if it is CR/level 6-10 it becomes a wight or a ghast, if it is CR/level 11-16 it becomes a ghost or a greater zombie, with the stat block of a flesh golem. If it is CR/level 17-20 it becomes a revenant and if it is CR 21+ or has more than three epic boons, it becomes a nightwalker.