Boon of the Reaper, Variant (5e Epic Boon)
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Wow, you have reached level 20 and are an undead! You must be so proud! Well, here's a boon just for you.
Boon of the Reaper
Prerequisite: Level 20 Undead
You are a fully fledged reaper and thus gain the following benefits:
You gain immunity to necrotic damage.
As an action you can impose your lingering presence onto those around you. Every creature within 5 feet of you takes 2d6 necrotic damage that ignores resistances, even absorption. When you do so they gain a level of lingering Death's Presence, (see spell-like ability). You regain hit points equal to the initial damage dealt. You can use this ability once per long rest
As a bonus action you can flood your weapons with your being. For 1 minute your weapons deal 2d6 necrotic damage that ignores resistance and immunity. If you get a critical success the necrotic energy lingers, giving a level of Death's Presence. You can use this ability once per short or long rest.
Death's Presence (spell-like ability)
Death's Presence has marked the creature for death.
A creature takes 2d6 necrotic damage. This initial necrotic damage cannot be resisted even with absorption.
Lingering: Until they are incapacitated, or until removed with a greater restoration (1 levels), the creature takes 1d6 necrotic damage, which is treated as if the creature is vulnerable if the have no resistance to necrotic, ignores resistance if they have it, or treats them as resistant if they are immune or higher. Lingering levels are stackable.
(Lingering is meant to remain without a duration to leave room for DM ruling of when lingering takes effect, though it automatically activates if they would get a new level of lingering)
(This boon was created for an OP campaign setting)