Cranium Rat (CR -)

Tiny Outsider
Alignment: Always neutral evil
Initiative: +2 (Dex); Senses: scent, Listen +6, and Spot +6

AC: 14 (+2 size, +2 Dex), touch 12, flat-footed 12
Hit Dice: 1/4d8 (1 hp)
Fort +2, Ref +4, Will +1
Speed: 30 ft.
Space: 2 1/2 ft./0 ft.
Base Attack +0; Grapple -12
Attack: Bite +5 melee
Full Attack: Bite +5 melee
Damage: Bite 1d3-4
Special Attacks/Actions:
Abilities: Str 2, Dex 15, Con 10, Int 2, Wis 12, Cha 2
Special Qualities: Scent, group mind, psionics
Feats: Alertness; Weapon Finesse (bite)
Skills: Balance +10, Climb +4, Hide +14, Listen +6, Move Silently +6, and Spot +6
Advancement: --
Climate/Terrain: Any land and underground
Organization: Swarm (5-100)
Treasure: None

Source: Converted

Group Mind (Ex): A single cranium rat is not much of a threat, but they gain power in numbers. Cranium rats have automatic telepathic contact with other cranium rats within 10'. For every five rats gathered in the same location, they gain a point of Int and a point of Cha, and for every ten rats they gain a point of Wis. The CR of a swarm of cranium rats is equal to their collective Int divided by 4 (for swarms of less than 25), or by 2 (for swarms of 25 and above).

Psionics (Sp): At Int 7 and above, cranium rats can manifest psionic powers. A swarm has the same number of powers, power points, and attack/defense modes as a psion of a level equal to their collective Int-6. (Alternatively, they can be treated as sorcerers of the same level.) They do not gain psionic feats, psicrystals, or extra skill points. The majority of powers manifested by cranium rats are clairsentient or telepathic, with psychoportive power in third place. Metacreative powers are very rare. Psychometabolic and psychokinetic powers are never manifested by cranium rats.

Area attacks against cranium rats can be treated as attacks against a single creature, with a single saving throw for the whole pack. For example, a fireball causing 14 points of damage will kill 14 rats (or seven if they make their save). However, mind-affecting spells can only affect one rat at a time, and the other rats will immediately break contact with the affected individual.

A swarm of 10 or more cranium rats is treated as having all-around vision, which gives them a +4 bonus to Spot and Search checks and prevents them from being flanked.

Sample power progression

The following is a pre-fabricated list of psionic powers for swarms of various sizes. The powers listed below are cumulative (i.e. each level also has the powers listed for all previous levels).

SwarmLevelIntWisChaPSPsPowers Discovered
25-291714 730 - catfall, detect psionics, know direction 1 - combat precognition
30-342815 841 - spider climb
35-393915 981 - object reading
40-444101610110 - distract, 2 - clairaudience/clairvoyance
46-495 111611192 - see invisibility
50-546121712240 - missive, 3 - remote viewing
55-597131713291 - empathy, 3 - false sensory input
60-648141814430 - telempathic projection, 4 - aura sight
65-699151815503 - danger sense, 4 - mindwipe
70-7410161916590 - daze, 5- sense psionics
75-7911171917682- aversion, 4- tailor memory, 5- mind probe
80-8412182018900 - float, 6 - precognition
85-89131920191011 - sense link, 5 - true seeing, 6 - remote view trap
90-94142021201147 - sequester
95-99152121211276 - ethereal jaunt, 7 - insanity
100+162222221552 - inflict pain, 8 - hypercognition