Cranium Controller

Keen Smell. The Cranium Controller has advantage on Wisdom (Perception) checks that rely on smell.

Pack Tactics. The Cranium Controller has advantage on an attack roll against a creature if at least one of the Controller's allies is within 5 feet of the creature and the ally isn't incapacitated.

Illumination. As a bonus action, the Cranium Controller can shed dim light from its brain in a 15-foot radius or extinguish the light.

Telepathic Shroud. The Cranium Controller is immune to any effect that would sense its emotions or read its thoughts, as well as to all divination spells. The Controller has advantage against be charmed or frightened.

Multiattack. The Controller makes 2 attacks. one with its Psychic jaws, the other with its Mystic slash.

Psychic Jaws. Melee/Ranged Weapon Attack: +5 to hit, reach 5 ft. or range 30ft., one target. Hit: 8 (1d8+3) piercing damage plus an extra 4 (1d8) psychic damage. If the target is a creature, it must succeed on a DC 14 Wisdom Saving throw or become's Stunned for the next 1 minute. at the end of each of its turns, it can make another Saving throw to break out of the Stunned condition. if a creature succeeds on the saving throw it takes half the psychic damage and isn't Stunned. 

Mystic Slash. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d6+3) slashing damage. plus an extra 2 (1d4) psychic damage

Controlling Thoughts. as a bonus action, the Controller can direct another cranium rat within 30ft of it to make an attack on a creature within 5ft of that cranium rat. this spends the reaction of the carnium rat in question.

Physic Shield (2/day). the Cranium Controller can use its reaction to give itself a +5 to its AC until the start of its next turn.