Brain Swarm
Huge • Aberration • Chaotic Evil
Armor Class 12
Hit Points 67 (9d12 + 9)
Speed 0 ft., fly 30 ft. (hover)
Initiative +2 (12)
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 1 (-5) | 14 (+2) | 12 (+1) | 16 (+3) | 13 (+1) | 9 (-1) |
Damage Resistances psychic; bludgeoning, piercing, slashing
Condition Immunities blinded, deafened, exhaustion, grappled, paralyzed, petrified, poisoned, prone, restrained, stunned, unconscious
Senses blindsight 90 ft. (blind beyond this radius), passive Perception 11
Languages -
CR 4 (XP 1,100; PB +2)
Bloodied – Thought Echoes. When the swarm becomes bloodied, it casts mirror image.
Limited Telepathy. The swarm can magically transmit simple messages and images to any creature within 30 feet of it that can understand a language. This form of telepathy doesn't allow the receiving creature to telepathically respond.
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny creature. The swarm can't regain hit points or gain temporary hit points.
Telepathic Garble. Creatures (except Aberrations) in a 15-foot emanation originating from the swarm have disadvantage on saving throws to maintain concentration.
Unusual Nature. The swarm doesn't require air, food, drink, or sleep.
ACTIONS
Memory Drain. Intelligence Saving Throw: DC 13, one creature within 30 feet of the swarm. Failure: 27 (6d8) psychic damage, or 13 (3d8) psychic damage if the swarm is bloodied. Additionally, the target's Intelligence score is reduced by 2 (minimum of 1), or 1 if the swarm is bloodied, and the target loses some of its memories. When a target Intelligence score is reduced to 1, it suffers from complete amnesia. This effect lasts until cured by a greater restoration or similar magic. Success: Half damage.
BONUS ACTIONS
Relive Memories. The swarm casts phantasmal force (spell save DC 13) targeting a creature it has affected with its Memory Drain. The illusion contains visions regarding the lost memories. While affected by the spell, the target is also frightened of the illusion.
Brain Swarm
Huge • Aberration • Chaotic Evil
Armor Class 11
Hit Points 32 (5d12)
Speed 0 ft., fly 30 ft. (hover)
Initiative +1 (11)
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 1 (-5) | 12 (+1) | 10 (+0) | 14 (+2) | 11 (+0) | 9 (-1) |
Damage Resistances psychic; bludgeoning, piercing, slashing
Condition Immunities blinded, deafened, exhaustion, grappled, paralyzed, petrified, poisoned, prone, restrained, stunned, unconscious
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 10
Languages -
CR 1 (XP 200; PB +2)
Bloodied – Thought Echoes. When the swarm becomes bloodied, it casts mirror image.
Limited Telepathy. The swarm can magically transmit simple messages and images to any creature within 30 feet of it that can understand a language. This form of telepathy doesn't allow the receiving creature to telepathically respond.
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny creature. The swarm can't regain hit points or gain temporary hit points.
Telepathic Garble. Creatures (except Aberrations) in a 10-foot emanation originating from the swarm have disadvantage on saving throws to maintain concentration.
Unusual Nature. The swarm doesn't require air, food, drink, or sleep.
ACTIONS
Memory Drain. Intelligence Saving Throw: DC 12, one creature within 30 feet of the swarm. Failure: 14 (4d6) psychic damage, or 7 (2d6) psychic damage if the swarm is bloodied. Additionally, the target's Intelligence score is reduced by 2 (minimum of 1), or 1 if the swarm is bloodied, and the target loses some of its memories. When a target Intelligence score is reduced to 1, it suffers from complete amnesia. This effect lasts until cured by a greater restoration or similar magic. Success: Half damage.
BONUS ACTIONS
Relive Memories (Recharges after a Rest). The swarm casts phantasmal force (spell save DC 12) targeting a creature it has affected with its Memory Drain. The illusion contains visions regarding the lost memories. While affected by the spell, the target is also frightened of the illusion.
Brain Swarm
Huge • Aberration • Chaotic Evil
Armor Class 13
Hit Points 119 (14d12 + 28)
Speed 0 ft., fly 30 ft. (hover)
Initiative +3 (13)
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 1 (-5) | 16 (+3) | 14 (+2) | 18 (+4) | 15 (+2) | 9 (-1) |
Damage Resistances psychic; bludgeoning, piercing, slashing
Condition Immunities blinded, deafened, exhaustion, grappled, paralyzed, petrified, poisoned, prone, restrained, stunned, unconscious
Senses blindsight 120 ft. (blind beyond this radius), passive Perception 12
Languages -
CR 7 (XP 2.900; PB +3)
Bloodied – Thought Echoes. When the swarm becomes bloodied, it casts mirror image.
Limited Telepathy. The swarm can magically transmit simple messages and images to any creature within 30 feet of it that can understand a language. This form of telepathy doesn't allow the receiving creature to telepathically respond.
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny creature. The swarm can't regain hit points or gain temporary hit points.
Telepathic Garble. Creatures (except Aberrations) in a 20-foot emanation originating from the swarm have disadvantage on saving throws to maintain concentration.
Unusual Nature. The swarm doesn't require air, food, drink, or sleep.
ACTIONS
Memory Drain. Intelligence Saving Throw: DC 15, one creature within 30 feet of the swarm. Failure: 44 (8d10) psychic damage, or 22 (4d10) psychic damage if the swarm is bloodied. Additionally, the target's Intelligence score is reduced by 2 (minimum of 1), or 1 if the swarm is bloodied, and the target loses some of its memories. When a target Intelligence score is reduced to 1, it suffers from complete amnesia. This effect lasts until cured by a greater restoration or similar magic. Success: Half damage.
BONUS ACTIONS
Relive Memories. The swarm casts phantasmal force (spell save DC 15) targeting a creature it has affected with its Memory Drain. The illusion contains visions regarding the lost memories. While affected by the spell, the target is also frightened of the illusion.
QUICK REFERENCE
USING MONSTER VARIANTS
Monster variants allow the GM to adjust encounters to better match the party’s strength, narrative needs, or world-building logic. A weaker variant may represent a juvenile, wounded, or lesser specimen, while a stronger variant can serve as a leader, champion, ancient creature, or apex predator.
Variants can be used to fine-tune difficulty without changing the core identity of the monster, making them ideal for scaling encounters, reinforcing hierarchy within a faction, or creating memorable boss-style enemies. You can even use the same stat block but different variants in the same encounter if you want.
Design Note. Each monster is primarily balanced around its normal version. Weaker and stronger variants are derived adjustments and may not always preserve every tactical nuance or “feel” of the original creature. GMs are encouraged to review variants carefully and adjust abilities or tactics as needed to best suit their table.