Demonic Cultivation

A Perverse imitation of traditional cultivation, demonic cultivation replaces the power of a cultivator's golden core with Resentful Energy, sourced from resentful spirits and walking corpses roaming the world. Demonic Cultivators sacrifice their personhood and temperament in their quest to earn power equal to a master cultivator. In many places, a demonic cultivator's fine control and understanding of resentful spirits might make him better suited to solving a cultivation problem, but the wider cultivation's world violent distrust of the Demonic path means it may never be recognised as a viable path. 

Resentful Energy Savant

Beginning when you select this school at 2nd level, the gold and time you must spend to copy a Necromancy spell into your spellbook is halved.

Overextension

Once you have used up all of your spell slots of a certain level, you can continue to cast necromancy spells, expending hit points instead. You expend HP equal to 5 x the level you are casting the spell at.

You are also able to cast resentful energy spells faster and more often than your other skills. Any necromancy spells with the duration "Instantaneous" that would usually take an action to cast, you can cast as a bonus action.

Fierce Corpses

At 6th level, you add the  Animate Dead  spell to your spellbook if it is not there already.

When you kill any creature with a necromancy spell, the creature is puppetted by your resentful energy. On your next turn, the creature rises as if you have cast Animate Dead on it. If you don't want to create a Fierce corpse, you must make a WIS saving throw DC 10 + the killing spell level + your corruption points. If you fail, the creature rises anyway and you have no control over it.

 The creature is under your control for 1 hour, after which it stops obeying any command you’ve given it. To maintain the control of the creature, you must cast Animate Dead  on the creature again before the hour ends. This use of the spell reasserts your control over up to four creatures you have animated with this spell, and from that point on the creature acts entirely like one created by Animate Dead .

Summon Resentful Spirit

If you do not already have it, add the spell [Tooltip Not Found]  to your spellbook.

You can cast [Tooltip Not Found] without expending a spell slot if there is a resentful spirit seeking to manifest within 60 ft, or a spirit seeking to haunt a living creature within 30ft. The spirit manifests as if cast at spell level 3 + its CR or player level in life, up to level 9.

If you attempt this but there is no spirit in range, you instead case[Tooltip Not Found] as normal at level 3, using a spell slot. You must use overextension if you don't have spell slots.

The creature is friendly to you and your companions at first. It has a will, to counteract whatever has caused it to remain as a resentful spirit. If you see the spirit doing something, you may attempt to control it from enacting its will as a reaction. You must make a CHA save against it, DC 10 + spell level + Spirit Will level, as drawn from the spirit will table. If you lose control of a spirit, it will primarily seek out to enact its will, but it may attack you and your companions if you stand in the way.

You may attempt to regain control over the spirit as an action on your turn. Make a Charisma (persuasion) against DC 10 + spell level + Spirit Will level.

You can dismiss a resentful spirit you are controlling as a bonus action.

 

Spirit Will Table
Compel not to do something it wants to do	+2
Compel to do something it doesn't actively want to do	+3
Compel in any way against spirit’s primary will	+5

Forge Spiritual Weapon

At level 14, you are able to bring your unique form of demonic cultivation to bear as a wondrous artefact. This artefact is unique to you, and only you can wield it to its full power.

When creating the artefact, the DM will roll one minor detrimental property (DMG 220), or assign (or agree with you) a similar level of detriment relevant to your actions as a demonic cultivator.

While you are attuned to this artefact, you can use it as a  +2 spell focus. At the time of forging your artefact, combine your spellcasting modifier and your proficiency bonus. Your artefact can store spells levels equal to that number at a time. You can cast any spell of 1st level or higher into the stone by touching it as the spell is cast. The spell has no effect, other than to be stored in the stone. If the stone can’t hold the spell, the spell is expended without effect. The level of the slot used to cast the spell determines how much space it uses. 

While your artefact is attuned,  you can cast any spell stored in it. The spell cast from the stone is no longer stored in it, freeing up space.