Diabolism

Study of the arcane is as old as the discovery of magic itself. However, where some choose to stay within the strict boundaries of the traditional schools, others plumb the depths of long forgotten lore, heavily restricted knowledge, or otherwise taboo subjects. Beyond even those, the constant, looming threat of Dondros to the south has always kept the practise of diabolism relegated to only the most dedicated, secretive, or obsessive practitioners.

Despite this, there are always those willing to risk the dangers and stigma of the practise, whether it be for the potential deals to be made with powerful Archfiends, an attempt to turn the hordes of bloodthirsty fiends to a more productive use, or other more inscrutable reasons. Most fail in the attempt, their souls lost to a deal gone bad or a demon turned loose. A few, however, manage to make something of the notoriously double-edged craft, always dancing a blade’s edge from utter damnation.

Infernal Study

When you choose this tradition at 2nd level, you learn to speak, read, and write Abyssal or Infernal (your choice). You also gain proficiency with calligrapher’s tools. Additionally, you gain proficiency in one of the following skills of your choice: Deception, Insight, Intimidation, or Persuasion. Your proficiency bonus is doubled for any ability checks you make using this skill.

Insidious Contracts

Starting at 2nd level, you gain the ability to create magical contracts, binding you and another willing creature, the signatory, into a pact. It takes 1 minute to draft a contract, and you may have a number of active contracts equal to your proficiency bonus. Additionally, you can only draft a number of contracts equal to your proficiency bonus between long rests. You cannot be the signatory of your own contracts.

When you use your Arcane Recovery you may regain additional spell slots of a combined level equal to your number of active contracts.

When you create a contract, the signatory may sacrifice any number of hit points, with an equal number being subtracted from their hit point maximum. The signatory of the contract may then choose any combination of boons from the following list:
Health. The signatory gains temporary hit points equal to twice the number sacrificed. Until the contract ends, these temporary hit points will be restored after a long rest.
Talent. For each 2 hit points sacrificed, the signatory can choose to add a +1 bonus to any ability check using a specific skill proficiency of their choice (chosen when the contract is made) up to a maximum of +5 per skill.
Resolve. For each 3 hit points sacrificed, the signatory can choose to add a +1 bonus to any saving throw using a specific ability score of their choice (chosen when the contract is made) up to a maximum of +5 per ability.
Fortune. For each 5 hit points sacrificed, the signatory can grant themselves advantage on an attack roll, ability check or saving throw of their choice per long rest.

Each hit point sacrificed can only be used to gain the benefit of a specific boon. The contract ends when you choose to do so as a bonus action, you die, or the contract is not renewed after 7 days. Once the contract ends, all boons are lost and the signatory’s hit point maximum is returned to normal, although no hit points are restored.

You gain the ability to grant additional boons at 6th, 10th and 14th level.

Clarity. At 6th level, the signatory may sacrifice 10 hit points to gain the ability to see in normal and magical darkness to a distance of 60 feet.
Warding. At 10th level, the signatory may sacrifice 15 hit points to gain advantage on saving throws against spells and magical effects.
Fortitude. At 14th level, the signatory may sacrifice 20 hit points to gain resistance to a damage type of their choice.

Cautious Practitioner

Beginning at 6th level you have gained an appreciation for the proper precautions when dealing with your fiendish ‘allies’. You add the magic circle spell to your spell book and can cast it without material components.

Additionally, when interacting with creatures trapped within a magic circle, you have advantage on any checks made against the imprisoned creature, including attack rolls and ability checks, and the creature has disadvantage on interactions directly involving you, such as saving throws or ability checks.

Arcane Leash

Starting at 10th level you can utilise the energy siphoned from your contracts to weaken creatures from the lower planes. When a fiend you can see makes a saving throw against a spell you cast, you can use your reaction to impose a penalty to the roll equal to your number of active contracts. You can use this ability after the outcome of the roll is revealed.

Additionally, as an action you can force a fiend you have summoned to make a Charisma saving throw, forcibly returning them to their plane of origin on a failure.

Fiendish Obeisance

Beginning at 14th level your understanding of the liminal gateways between planes has grown to an unparalleled degree. When you cast a spell that summons fiends you may ignore the concentration feature of the spell. Attempting to cast another spell from the conjuration school that requires concentration ends the first spell as though your concentration had been broken.