Secrets so grim that mortals start vomitting blood, evil so horrible that animals shun it, efficiency so micromanaged, that the fiercest machineries of law stand in awe.

Supposedly, this work of systematic evil has been written by Asmodeus himself, to put down the lawful stance of evil, to be opposed by the Books of Vile Darkness and Exalted Deeds. 
This pure manifestation of the searing endless torment to be found for souls within Baator, is a masterpiece of evil, said to be able to turn mortals into devils, and promote devils up to archdevil status.

This bound tome is finely crafted out of the hide of monstrosities, infernal paper that puts sheets of metal to shame, and a runic font of truly EVIL origins that makes celestials weep blood. 

Like the Book of Vile Darkness, nature can’t abide the Tome of Baatorian Law’s presence. Ordinary plants wither in its presence, animals are unwilling to approach it, and the book gradually destroys whatever it touches. Even stone cracks and turns to powder if the book rests on it long enough. There is always a slight smell of brimstone around the book, and non magical objects around the book tear, combust or whither and fall apart. Shrieks of the tormented can be heard while the book is opened.

A creature attuned to the book must spend 66 hours and 6 minutes reading and studying it to digest its contents and reap its benefits. The creature can then freely modify the book’s contents, provided that those modifications advance evil and expand the lore already contained within.

Whenever a non-evil creature attunes to the Tome of Baatorian Law, that creature must make a DC 17 Charisma saving throw. On a failed save, the creature’s alignment changes to lawful evil.

The Tome of Baatorian Law remains with you only as long as you strive to work evil in the world. If you fail to perform at least one evil act within the span of 10 days, or if you willingly perform a good act that doesn't benefit your selfish goals, the book disappears. If you die while attuned to the book, Asmodeus himself claims your soul. You can’t be restored to life by any means while your soul remains imprisoned.

Random Properties

The Tome of Baatorian Law has the following random properties:

• 3 minor beneficial properties
• 1 major beneficial property
• 3 minor detrimental properties
• 2 major detrimental properties

Adjusted Ability Scores

After you spend the requisite amount of time reading and studying the book, one ability score of your choice increases by 2, to a maximum of 24. Another ability score of your choice decreases by 2, to a minimum of 3. The book can’t adjust your ability scores again.

Mark of Baator

After you spend the requisite amount of time reading and studying the book, you acquire a physical manifestations of the devils that mark you as one of their own. You receive one or more of the following traits of the DM's choice: red glowing eyes, snake eyes, a slitted tongue, devilish horns, goat legs, a devilish tail, an echoing voice, a flat nose with slits for nostrils, canine-like teeth, crying blood instead of tears.

From then on, the paladin's divine sense feature, and spells that would detect fiends register you as such.

The mark of baator grants you advantage on Charisma (Persuasion) checks made to interact with fiends and Charisma (Intimidation) checks made to interact with non-fiends.

Authority of the Dark Lord

While you are attuned to the book and holding it, you can use an action to cast Command at base level on a fiend (save DC 18) at will.

The book has three charges, which reset after a tenday. By expending a charge of this item, as an action you can cast Geas or Dominate Monster on a devil below rank archdevil, DC 18.

By expending two charges, you can summon the devil spirit only bound to this book, the statblock of which the DM decides on and keeps.

Infernal Lore

You can reference the Tome of Baatorian Law whenever you make an Intelligence check to recall information about some aspect of fiends, such as evil rituals, cults, or their homes, the Abyss or Baator. When you do so, double your proficiency bonus on that check. 

This book can also be used as a spellbook.

Destroying the Book 

Pages ripped from the book turn to ashes instantly as the page reappears as if molten out of fire within the book, smelling of the infernal ink like on the day it was written.

A 9th level spellslot used with a spell that deals radiant damage on the book, destroys it, 1d6 x 66 days after which it reforms in Nessus.

A creature attuned to the book for one hundred years can unearth a phrase hidden in the original text that, when translated to Celestial and spoken aloud, destroys both the speaker and the book in a blinding flash of radiance. However, as long as Asmodeus is alive, the book reforms 1d10 × 66 years later within Nessus.

Hellish Content

The Tome of Baatorian Law was written by Asmodeus with a single goal in mind: tempting mortals. It can contain content like Rituals, information on cults and otherworldly creatures, and sometimes even spells.

Notes: Advantage: Persuasion, Advantage: Intimidation, Expertise: Intelligence Ability Checks, Damage, Control, Buff, Debuff, Utility, Combat, Cursed