Thessamere, the Ledger of Sighs

medium fiend (devil), Lawful Evil · CR 15

by Ledgerhand

Armor Class: 19

Hit Points: 247

Speed: 30 ft., fly 60 ft.

Saving Throws: dexterity, constitution, wisdom, charisma

Skills: Deception +12, Insight +9, Perception +9, Persuasion +12

Damage Resistances: Bludgeoning (nonmagical), Cold, Piercing (nonmagical), Slashing (nonmagical)

Damage Immunities: Fire, Poison

Condition Immunities: Charmed, Frightened, Poisoned

Senses: darkvision 120 ft., truesight 60 ft., passive Perception 19

Languages: Common, Abyssal, Draconic, Infernal

Challenge: 15 (13,000 XP)

STR 16 (+3)

DEX 20 (+5)

CON 20 (+5)

INT 22 (+6)

WIS 19 (+4)

CHA 24 (+7)

Traits

Magic Resistance. Thessamere has advantage on saving throws against spells and other magical effects.
Devil’s Sight. Magical darkness does not impede Thessamere’s darkvision.
Contract-Bound. Thessamere cannot tell a deliberate lie, and cannot attack a creature that has an unbroken agreement with him. He is exhaustively literal: any ambiguity in an agreement resolves in his favour, and he will point out the ambiguity afterwards, at length.
Ledger of Sighs. Thessamere carries a ledger that cannot be destroyed while he lives. As an action he can read a name from it; if that creature is on the same plane, it knows it has been read, and has disadvantage on the next saving throw it makes against Thessamere before the end of its next long rest.

Its spellcasting ability is Charisma (spell save DC 20, +12 to hit with spell attacks).

Cantrips. Charm Person, Counterspell, Detect Magic, Dispel Magic, Dominate Person, Scrying, Wall of Fire

Multiattack. Thessamere makes three Quill of Judgment attacks, or makes one Quill of Judgment attack and casts a spell of 3rd level or lower.
Quill of Judgment. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 3d6 + 5 piercing damage. Thessamere writes the wound into the ledger as it is made. A creature reduced to 0 hit points by this attack cannot be restored to life by any spell of 5th level or lower until the debt recorded against its name is settled.
Sigil of Arrears (Recharge 5-6). Hit: 6d8 psychic damage. The target must succeed on a DC 20 Wisdom saving throw or be frightened (save ends). It takes half as much damage on a successful one. Every promise the targets have broken is read aloud at once. Each creature within 20 feet of Thessamere must make the saving throw.

Amend the Terms. Thessamere strikes out a line in the ledger. One creature he can see within 60 feet that is charmed or frightened by him takes 14 (4d6) psychic damage, and the condition ends.

Clause of Recompense. Thessamere records the offence. The triggering creature must succeed on a DC 20 Charisma saving throw or take 21 (6d6) necrotic damage, and Thessamere gains temporary hit points equal to the damage dealt.

Quill.
Read the Name. Thessamere reads one name aloud from the ledger. That creature must succeed on a DC 20 Wisdom saving throw or have disadvantage on the next attack roll or saving throw it makes before the end of its next turn.
Terms Renegotiated. Thessamere teleports up to 60 feet to an unoccupied space he can see and exchanges positions with one willing creature that has an agreement with him. Both creatures take 10 (3d6) psychic damage from the sudden revision.

Lair Action 1. The floor of the hall becomes a written page. Each creature of Thessamere's choice within 60 feet must succeed on a DC 20 Dexterity saving throw or be restrained until initiative count 20 on the following round as clauses close around its feet.

Regional Effect 1. Within 3 miles of Thessamere's lair, no creature can knowingly break a spoken promise without feeling it: the offender takes 5 (1d10) psychic damage the moment the promise is broken, and Thessamere knows the offender's name and direction.
Regional Effect 2. Ink will not dry within 1 mile of the lair. Written agreements smear, ledgers run, and any document signed in the region is legally void everywhere except in Thessamere's hand, where it is perfectly legible.