Cranium Rat King

Shapechanger. The Rat King can polymorph as a bonus action into a rat-human hybrid form, or giant rat form. All stats aside from its size stay the same. Any equipment it wears or carries is not transformed.

Spellcasting (Psionics). The Cranium Rat King is an innate spellcaster. Its spellcasting ability is Intelligence (spell save DC 13). As long as it is at or above half hit points the Cranium Rat King has the following spells.
Cantrips (at will): Command, Comprehend languages, detect thoughts
1/Day each: Confusion, Dominate monster

Telepathic Shroud, As long as it is at or above half hit points, the Cranium Rat King is immune to any effect that would sense its emotions or read it's thoughts, as well as to all divination spells

Keen Smell. The Cranium Rat King has advantage on Wisdom (perception) checks that rely on smell.

Illumination. As a bonus action, the Cranium Rat King can shed dim light from its brains in a 5ft to 20ft radius (and dim light for an additional number of feet equal to the chosen radius), or extinguish the light.

Multiattack. The Cranium Rat King makes three attacks only one of which can be a bites attack.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit:  4 (2d4) slashing damage. 

Bites. Melee Weapon Attack: +5 to hit, range 5 ft., one target. Hit: 14 (4d6) [damage type] damage.

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