Elemental Cadaver (Necrograft)

You can manipulate one of the three elements: fire, frost, or lightning.  This necrograft is generally gained in one of two ways.  You ritualistically consumed the corpse of someone that was either burned to death, frozen to death, or slain by lightning. Or, you were killed by one of the elements and were resurrected.

Choose one of the three elements; this affects the type of damage that this necrograft’s abilities deal.

If you ritualistically consumed a corpse, the details of how you acquired it are 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. Any spells that you cast through this necrograft require no verbal, somatic, or material components, even expensive ones. 

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.

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.

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.

Stage 1

You can launch an Elemental Bolt at will.  This acts like the Firebolt cantrip, but does damage of the element you selected.                         

You gain the Elemental Surge ability.  This has one of two possible effects.

You can use Elemental Surge to strengthen your unarmed strikes.  This requires no action.  Until the end of your turn, your unarmed strikes deal an additional 1d4 of your element damage.

You can also use Elemental Surge as an action to unleash a wave of energy.  This acts as Burning Hands cast with a level 1 slot, but does damage of the element you selected. 

You can use Elemental Surge twice between rests. When you finish a short or long rest, you regain your expended uses.

Stage 2

Elemental Bolt does additional damage equal to your Constitution modifier.

Elemental Surge now deals an additional 1d6 of your element damage when you use it to strengthen your unarmed attacks.  When you use it to unleash a wave of energy, it acts as Burning Hands cast with a level 2 slot.  Additionally, you can change its area of effect to a 30 foot line.

You gain resistance to your element damage.

Stage 3

You gain the Corpse Element ability.  The abilities from this necrograft can deal half element damage and half necrotic damage.

Elemental Bolt does half damage when it misses.

Elemental Surge now deals an additional 1d8 of your element damage when you use it to strengthen your unarmed attacks.

When you use it to unleash a wave of energy, you can instead use Elemental Surge as a bonus action.  It does damage as Burning Hands cast with a level 3 slot.

Stage 4

Elemental Surge now deals an additional 1d10 of your element damage when you use it to strengthen your unarmed attacks.

You can use your action to assault your foes with a tremendous blast of energy.  This Elemental Wrath ability acts as either Fireball or Lightning Bolt cast with a level 5 slot or Immolation, but does damage of your chosen element.  Additionally, affected creatures that fail their saving throw fall prone.  Once you use this feature, you can’t use it again until you finish a long rest.

You can increase the strength of Elemental Wrath by also spending uses of Elemental Surge.  Each use of Elemental Surge you spend increases the damage of Elemental Wrath by 2d6.  If you reproduce Immolation, only the initial damage is increased.  You cannot use Elemental Wrath and Elemental Surge on the same turn.

Finally, when you use Elemental Surge to unleash a wave of energy, it does damage as Burning Hands cast with a level 4 slot and also empowers your unarmed attacks.

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.