Source: Undead Classes
Author: Mandramas

What happens when you are
Spectral Rebirth
When you choose this archetype at 3rd level, you are tainted with a vengeful wrath that will mark your soul. The next time you die, you can choose to rebirth as a undead creature. (Alternatively, you can choose to wait to be returned to life by other means). If you back as an undead, you gain the following features from that moment:
- You are considered an undead creature, and lost the humanoid type. This means that you are immune to spells that target only humanoids (like charm person) but you are now affected by spells that targets undead.
- You have immunity to Necrotic and Poison damage.
- You have vulnerability to Radiant damange.
- You have inmunity to conditions Exhaustion and Poisoned
Life Drain
Starting at 3rd level, you’re able to steal your enemy. When you hit a creature with a weapon attack, you can choose to deal an extra 1d8 necrotic damage to the target. You gain temporary hit points equal to the extra damage dealt provided that the target isn’t a construct or an undead. Once you use this feature, you must finish a short or long rest before you can use it again. You will lose your temporary hit points when you finish a short or long rest, or when you end your turn under direct sunlight.
Dwell in Darkness
Starting from 3rd level, you have darkvision 60 ft. While in sunlight, you have disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Spectral Form
Starting at 7th level, your body became an semisubstancial ghost permanently. You gain the following features:
- Item restrictions: You can't wear armor or clothes, wield weapons, or carry other items in your body like bags, belts, rings or cloak, unless they are magical and are attunned to you. You still can use other items as long as they you don't carry it in your body. You can still lift objects and carry them a short run, but eventually they slip your body and fall to the ground. The DM can ask for Constitution checks to maintain your solidity enougth if you want to try more than a round.
- Necrotic Fulcrum: Everytime you deal bludgeoning, slashing or piercing damage with an attack roll, you can choose to deal instead necrotic damage.
- Nothing will stop me: You can move through other creatures and objects as if they were difficult terrain. You ignore non magical difficult terrain. You take 1d10 force damage if you end your turn inside an object.
- Beyond your grasp: You have resistance from Bludgeoning, Piercing, and Slashing damage from Nonmagical Attacks. You have inmunity to conditions Grappled, Prone or Restrained.
Advanced Life Drain
Starting from 10th level, when you use your life drain feature, if you choose to inflict all the damage as necrotic damage, you gain life equal to the total damage. Also, drained creatre must succeed on a DC Constitution saving throw or can't heal himself until the creature finishes a long rest. The save DC = 8 + your proficiency bonus + your Strength modifier.
You can use your life drain feature twice until you do short or long rest.
Advanced Spectral Form
Starting 15th level, you have resistance to Acid, Cold, Fire, Lightning and Thunder damage. You have immunity to Frightened, Paralyzed, Petrified or Blinded conditions.
Fatal Drain
Beginning 18th level, you can use your Life Drain once each turn.