Wight Heart (Necrograft)

You do not remove your own heart, but implant next to it the heart of a slain wight.  You always feel its icy presence.

Whether you have to make a Medicine check to implant the heart and whether you had to go on a quest to acquire the heart are details best left up to your GM.

You can expend a spell slot to activate the necrograft.  The more powerful the spell slot is, the more powerful the necrograft is.  When you expend a spell slot, the necrograft is active for 24 hours or until you finish a long rest, whichever comes first.  If you are a warlock, any spell slot that you expend to cast this spell is not regained until you finish a long rest.

The necrograft has four different power levels: Stage 1, Stage 2, Stage 3, and the most powerful, Stage 4.  The benefits are cumulative, if you activate the necrograft at Stage 2, you also gain the benefits described in Stage 1.  The DC of any features gained through this necrograft is your spell DC.

Activating the necrograft at Stage 1 requires expending a spell slot of at least 3rd level.

Activating the necrograft at Stage 2 requires expending a spell slot of at least 5th level.

Activating the necrograft at Stage 3 requires expending a spell slot of at least 7th level. 

Activating the necrograft at Stage 4 requires expending a 9th level spell slot.

At any given time, you can have up to four necrografts active.  One cannot exceed Stage 1, one can be up to Stage 2, one can be up to Stage 3, and one can be up to Stage 4.

This spell was originally designed as part of the Necrografter class, which can be found on DnDBeyond. It is intended to be used with the spell Unhallowed Arts, which can also be found on DnDBeyond.

Stage 1

Once per round, you can make a Wight Strike when you hit a creature with an unarmed strike.  An affected creature takes an additional Unhallowed Arts die of necrotic damage and must make a Constitution saving throw or deal half damage with its next successful weapon attack before the end of its next turn.

You use Wight Strike three times between rests. When you finish a short or long rest, you regain your expended uses.

When you use Wight Strike, you cannot simultaneously use Ghoul Strike (from the Ghoul Claws necrograft) or Profane Smite (from the Paladin's Tomb necrograft).

You also gain some of a wight’s ability to ambush its prey.  You gain proficiency in Stealth.

Stage 2

You gain the Wight’s Spite ability. The first unarmed attack you hit with on each of your turns deals an additional 1d6 plus your Constitution modifier necrotic damage.

A creature that fails its saving throw against Wight Strike deals half damage with weapon attacks until the end of its next turn. 

Stage 3

Your deadliest attacks become even more powerful. A creature that you critically hit with an unarmed strike cannot take reactions or regain any hit points until the end of your next turn.

If a creature fails its saving throw against Wight Strike, you gain 1d4+5 temporary hit points as you drain some of its life.

Your necrotic damage ignores any resistance that the target has.

Stage 4

You gain the Darkest Heart ability. You can spend a bonus action to make your implanted wight heart beat for 1 minute, filling you with unlife.  While it beats, the damage of Wight’s Spite is doubled, and you gain advantage on Constitution saving throws.  In addition, you can use Wight Strike every round.  These uses do not count against the three times between rests limit. Once you use this feature, you can’t use it again until you finish a long rest.

You roll two additional dice when you use Wight Strike, and you gain 1d6+5 temporary hit points when a creature fails its saving throw against Wight Strike. 

Your necrotic damage affects creature immune to necrotic as though they instead have resistance to it.

Other necrografts can be found on DnDBeyond.  Here is the complete list:

Abomination Gut: You can vomit acid and belch poison.

Bonemail: You can better protect yourself and your allies.

Bone Spikes: You gain long-range attacks and can retaliate against foes.

Elemental Cadaver: You can channel fire, frost, or lightning.

Ghoul Claws: You can gouge and paralyze your foes as well as swim through the ground.

Mummified Eye: You gain a fearsome gaze, bonuses to initiative, and access to some divination spells. 

Lich’s Skull: You heighten your mental defenses and gain minor spellcasting plus knowledge.

Paladin’s Tomb: You’re the opposite of a holy man, but you can fight like one.

Two Corpses in One Grave: Sharing your body with another soul, you can change your appearance and shock your opponents with a hideous metamorphosis.

Wight Heart: Your attacks deal extra damage and can weaken your enemies.

Vampiric Grace: You can move fast, crawl on walls, and drink the blood of your foes.

Vampiric Soul: You can bend the minds of others to your will and call creatures of the night to serve your bidding.

Zombie Hulk: You can increase your size and use special melee attacks.