Sigil of the Reaper

Essense of Undeath: You gain resistance to necrotic damage while attuned to the sigil. You are also able to faintly see spirits and other otherwordly beings. As a bonus action on your turn, you may choose to see into the Ethereal plane, but become blind to the Material, as your eyes turns ghostly blue. As another bonus action, you may remove this effect from yourself.

Sow: As a bonus action on your turn, you may enter a state of "Sowing" for 36 seconds, regardless if you go unconsious or other status effects, starting with 1 stack of Sow. As a bonus action on subsequent turns while in a state of Sowing, you may increase your Sow stacks by 1. Whenever you make an attack roll, you gain a +1 bonus for every stack of Sow. Whenever you hit a creature with an attack, you deal 1d10 extra necrotic damage to it for every stack of Sow. You may only enter a state of "Sowing" once per long rest.

Reap: Whenever you leave a state of Sowing, you lose 20 hit points for every stack of Sow that you had. This is not damage taken, so effects like Death ward will not trigger from it. If this health loss reduces your hit points to 0, you instantly die.