Animal Lord, Mouse King

Family: Animal Lords

This dog-sized mouse has a hairless tail and copper eyes. Its fur is ash-white with streaks of dark gray across its back in an asymmetrical pattern.

Small fey (shapechanger), neutral

Armor Class 17 (natural armor)
Hit Points 150 (20d6 + 80)
Speed 40 ft., climb 30 ft.

18 (+4) 23 (+6) 18 (+4) 20 (+5) 18 (+4) 18 (+4)

Saving Throws Dexterity +10, Constitution +8, Wisdom +8, Charisma +8
Skills Acrobatics +14, Deception +8, Nature +9, Persuasion +8, Sleight of Hand +14, Stealth +14, Survival +8
Damage Resistances lightning; bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities poison, psychic
Condition Immunities charmed, exhaustion, frightened, incapacitated, poisoned, stunned
Senses darkvision 120 ft., passive Perception 14
Languages all, telepathy 120 ft.
Challenge 11 (7,200 XP)

Special Traits

  • Keen Sight. The Mouse King has advantage on Wisdom (Perception) checks that rely on sight.
  • Legendary Resistance (3/day). If the Mouse King fails a saving throw, he can choose to succeed instead.
  • Magic Resistance. The Mouse King has advantage on saving throws against spells and other magical effects.
  • Magic Weapons. The Mouse King’s weapon attacks are magical.
  • Rejuvenation. If he dies, the Mouse King’s soul reforms on the Astral Plane. In 1d6 days, it inhabits the body of another mouse or rat on the Material Plane which becomes the Mouse King with all of the hp and abilities thereof. Only killing every mouse and rat on the Material Plane will prevent this trait from functioning.
  • Rodent Passivism. No rodents, ratfolk, or wererats can willingly attack the Mouse King. They can be forced to do so through magical means.
  • Shapechanger. The Mouse King can use his action to polymorph into a Medium black-haired human woman with dark skin and copper eyes or a Small white-haired halfling man with pale skin, dark eyes and a long moustache, a Medium mouse-humanoid hybrid, or back into his true Small mouse form. His statistics, other than his size, are the same in each form with the exception that only his hybrid and true forms retain his climbing speed. Any equipment he is wearing or carrying transforms with him.
  • Speak with Rodents. The Mouse King can communicate with rodents as if they shared a language.
  • Special Equipment. The Mouse King wears a ring of spell turning.
  • Innate Spellcasting. The Mouse King’s innate spellcasting ability is Charisma (spell save DC 16). He can innately cast the following spells, requiring no material components:


  • Multiattack. In mouse form, the Mouse King makes two bite attacks. In humanoid form, he makes three king’s blade attacks. In hybrid form, he makes three attacks: two with his king’s blade and one with his bite.
  • King’s Blade (Humanoid or Hybrid Form Only). Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 6) piercing damage.
  • Bite (Mouse or Hybrid Form Only). Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) piercing damage plus 7 (2d6) poison damage. If the target is a creature, it must succeed on a DC 16 Constitution saving throw or become poisoned for 1 hour.
  • Summon Rodents (2/day). The Mouse King magically calls 2d4 swarms of rats. In an urban environment, he can call 1d4 wererats instead. The called creatures arrive in 1d4 rounds, acting as allies of the Mouse King and obeying his spoken commands. The creatures remain for 1 hour, until the Mouse King dies, or until the Mouse King dismisses them as a bonus action.

Legendary Actions

The Mouse King can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Mouse King regains spent legendary actions at the start of his turn.

  • King’s Blade. The Mouse King makes one king’s blade attack.
  • Move. The Mouse King moves up to his speed without provoking opportunity attacks.
  • Quick Casting (Costs 3 Actions). The Mouse King casts one innate spell.

The Mouse King’s Lair

The Mouse King lives in the alleys and sewers of cities. Cities with a high amount of underground and criminal activity are especially attractive to the Mouse King. His lair is full of twisting sewer pipes of various sizes and dark alleyways leading to dead ends or in circles. Some of the pipes and alleyways lead to sewers and alleys in different cities, placing the Mouse King’s lair in a space between cities.

Lair Actions

On initiative count 20 (losing initiative ties), the Mouse King takes a lair action to cause one of the following effects; he can’t use the same effect two rounds in a row:

  • The Mouse King raises his arms and squeals, calling swarms of rodents from the environment to trip his enemies. Each creature within 60 feet of the Mouse King must succeed on a DC 16 Dexterity saving throw or be knocked prone.
  • The Mouse King chooses a point within 120 feet that he can see. A wave of spectral rodents emerges from the ground at that point and attacks all creatures in a 30-foot-radius centered on that point. Each creature in that area must succeed on a DC 16 Constitution saving throw or take 10 (3d6) poison damage and be poisoned for 1 minute.
  • Each creature of the Mouse King’s choice within 60 feet of him must make a DC 16 Wisdom saving throw. On a failure, the creature is transformed into a mouse as if affected by the polymorph spell. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to this effect for the next 24 hours.

Regional Effects

The section of a city containing the Mouse King’s lair is warped by his magic, which creates one or more of the following effects:

  • The area within 1 mile of the lair attracts hundreds of mice and rats. The Mouse King can choose to see or hear through the senses of any mouse or rat in this area and can speak through it while doing so.
  • Mice and rats within 1 mile of the lair are more resistant to disease. They never catch, carry, or spread any diseases unless the Mouse King wishes it.
  • Illicit deals are easier to hide near the lair. Dexterity (Sleight of Hand) checks made within 1 mile of the lair have advantage, and Wisdom (Perception) or Intelligence (Investigation) checks made to notice or find illegal dealings have disadvantage. If the Mouse King dies, these effects fade over the course of 1d10 days.


King of Rodents. The Mouse King is the King of all rodents, and he spends his days looking after the concerns of rodents on the Material, Astral, and Ethereal Planes. When slain, he is reborn within a week. His people’s ability to rapidly multiply leaves him with plenty of resources to defend his kind against the machinations of demon lords.

In the Company of Thieves. The Mouse King can always be found at the head of a guild of thieves. He schemes to make sure his wealth continues to grow, which often means entering into conflict with other gangs.

Civic-Minded Scoundrel. When it comes to making money, he takes into account what is best for the long-term prosperity of the city in which he operates, which he rightly believes is integral to his own success and that of his subjects. He is a great proponent of trade of all kinds, and his subjects have found their way to every corner of the world in the company of sailors, merchants, and drovers.

Section 15: Copyright Notice

Creature Codex. © 2018 Open Design LLC; Authors Wolfgang Baur, Dan Dillon, Richard Green, James Haeck, Chris Harris, Jeremy Hochhalter, James Introcaso, Chris Lockey, Shawn Merwin, and Jon Sawatsky.

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