Skitterthrone, Verminlord of the Nine Gutters

Traits

• Shapechanger. Skitterthrone can use its action to polymorph into a swarm of rats, or back into its true form. Its statistics are the same in each form, except that in swarm form it can move through any opening large enough for a Tiny creature without squeezing. Anything it is carrying is subsumed into the swarm. It reverts to its true form if it dies.
• Debt-Bound. A creature that willingly accepts a bargain from Skitterthrone is marked until the debt is paid. While marked, it has disadvantage on saving throws against Skitterthrone's abilities, and Skitterthrone always knows the direction to it while on the same plane of existence.
• Gutter Stride. Skitterthrone can move through a space as narrow as one inch wide without squeezing, and difficult terrain made of refuse, mud, or standing water costs it no extra movement.
• Magic Resistance. Skitterthrone has advantage on saving throws against spells and other magical effects.

Innate Spellcasting

Its spellcasting ability is Charisma (spell save DC 17, +9 to hit with spell attacks).

• Cantrips. Charm Person, Detect Magic, Disguise Self, Dominate Person, Fear, Plane Shift

Actions

• Multiattack. Skitterthrone makes one Tithe-Hook attack and two Gnawing Bite attacks.
• Tithe-Hook. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 2d8 + 5 piercing damage. Skitterthrone sinks a rusted tithe-hook into the target and drags what it owes. On a hit the target also takes 9 (2d8) necrotic damage, and if it is Large or smaller Skitterthrone pulls it up to 10 feet toward itself.
• Gnawing Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 2d6 + 5 piercing damage. A hundred small mouths open along Skitterthrone's forelimb and close at once. A creature bitten this way cannot regain hit points until the end of its next turn.
• Ledger of Debts. Hit: 6d6 psychic damage. The target must succeed on a DC 17 Wisdom saving throw, taking half as much damage on a successful one. Skitterthrone reads aloud from a ledger of every promise the listeners have broken. Each creature of its choice within 30 feet that can hear it must make the save.

Bonus Actions

• Scurry. Skitterthrone takes the Disengage or Hide action. If it ends this movement in dim light or darkness, it also gains half cover until the start of its next turn.
• Call the Tally. Skitterthrone names one creature it can see within 60 feet that owes it a debt. That creature must succeed on a DC 17 Wisdom saving throw or be frightened of Skitterthrone until the end of its next turn.

Reactions

• Collector's Due. Skitterthrone claims the debt in full. It gains 15 temporary hit points, and the creature cannot be restored to life by any spell of 4th level or lower until Skitterthrone is destroyed.
• Rat-Cloak Parry. A pelt of living rats surges over the wound. Skitterthrone adds 4 to its AC against that attack, potentially causing it to miss.

Legendary Actions

• Tithe.
• Flood the Gutter. Filthy water bursts from every drain within 20 feet of Skitterthrone. Each creature in that area must succeed on a DC 17 Strength saving throw or be knocked prone and take 17 (5d6) acid damage.
• Read the Debt. Skitterthrone names aloud one thing a creature it can see has failed to repay. That creature must succeed on a DC 17 Charisma saving throw or be charmed by Skitterthrone until the end of its next turn.

Lair Actions

• Sluice Gates. A gate slams somewhere in the dark and the water changes course. Each creature on the ground within 30 feet of a channel must succeed on a DC 15 Strength saving throw or be swept 20 feet along it and knocked prone.
• The Nine Names. Rats in the walls speak in unison, reciting the debts of one creature Skitterthrone can see. That creature must succeed on a DC 15 Wisdom saving throw or have disadvantage on attack rolls until initiative count 20 of the next round.

Regional Effects

• The Water Remembers. Within 1 mile of Skitterthrone's lair, still water shows not the viewer's reflection but the face of someone they have wronged. Creatures that drink from it must succeed on a DC 15 Wisdom saving throw or be unable to lie for 1 hour.
• Vermin Census. Rats within 6 miles of the lair are unnaturally orderly, moving in counted ranks and gathering at doorways to tally who passes. Skitterthrone learns the name of any creature that spends a night within this region.