# [Cranium Rat](Rules\Source\bestiary\aberration/cranium-rat-mpmm.md)
*Source: Mordenkainen Presents: Monsters of the Multiverse p. 83*
## Cranium Rat
Mind flayers create cranium rats by bombarding rats with psionic energy. Cranium rats are somewhat smarter than ordinary rats and behave as such. If enough cranium rats come together to form a swarm, they merge their minds into a single intelligence with the accumulated memories of all the swarm's constituents. The rats become smarter as a result, and retain their heightened intelligence for as long as the swarm persists. The swarm also awakens latent psionic abilities implanted within each cranium rat by its mind flayer creators, bestowing upon the swarm psionic powers.
A single cranium rat uses its natural telepathy to communicate hunger, fear, and other base emotions. A swarm of cranium rats communicating telepathically "speaks" as one creature, often referring to itself using the collective pronouns "we" and "us." Some mind flayer colonies use cranium rats as spies. The rats invade communities and act as eyes and ears for the colony's elder brain, transmitting their thoughts when they swarm and are within range of the elder brain's telepathy.
```statblock
"name": "Cranium Rat (MPMM)"
"size": "Tiny"
"type": "aberration"
"alignment": "Unaligned"
"ac": !!int "12"
"hp": !!int "2"
"hit_dice": "1d4"
"modifier": !!int "2"
"stats":
- !!int "2"
- !!int "14"
- !!int "10"
- !!int "4"
- !!int "11"
- !!int "8"
"speed": "30 ft."
"senses": "[darkvision](/Rules/Source/senses.md#Darkvision) 30 ft., passive Perception\
\ 10"
"languages": "telepathy 30 ft."
"cr": "0"
"traits":
- "desc": "The cranium rat is immune to any effect that would sense its emotions\
\ or read its thoughts, as well as to all divination spells."
"name": "Telepathic Shroud"
"actions":
- "desc": "*Melee Weapon Attack:* +4 to hit, reach 5 ft., one target. *Hit:* 1 piercing\
\ damage."
"name": "Bite"
"bonus_actions":
- "desc": "The cranium rat sheds dim light from its exposed brain in a 5-foot radius\
\ or extinguishes the light."
"name": "Illumination"
"source":
- "MPMM"
"image": "/Rules/Source/bestiary/aberration/token/cranium-rat-mpmm.webp"
```
^statblock
## Environment
underdark, urban