monster

Elder Brain Dragon

CR 22

Gargantuan Aberration, Lawful Evil

Reveal Stat Block

Armor Class

17 (natural armor)

Hit Points

350 (20d20 + 140)

Speed

40 ft., fly 80 ft. (hover)

str

dex

con

int

wis

cha

Traits

Legendary Resistance (4/Day).If the dragon fails a saving throw, it can choose to succeed instead.

Siege Monster.The dragon deals double damage to objects and structures.

Unusual Nature.The dragon doesn't require air or sleep.

Actions

Multiattack.The dragon makes one Bite attack, two Claw attacks, and one Tentacle attack.

Bite.mw 15 to hit, reach 15 ft., one target. ({@damage 2d10 + 8) piercing damage plus 11 (2d10) psychic damage.

Claw.mw 15 to hit, reach 10 ft., one target. ({@damage 1d6 + 8) slashing damage.

Tentacle.mw 15 to hit, reach 15 ft., one creature. ({@damage 1d8 + 8) psychic damage. If the target is Huge or smaller, it is grappled (escape 18). The dragon can have up to four targets grappled at a time.

Tadpole Brine Breath 5.The dragon exhales brine in a 120-foot line that is 15 feet wide. Each creature in that area must make a 22 Constitution saving throw, taking 55 (10d10) psychic damage on a failed save, or half as much damage on a successful one. On a success or failure, if the creature isn't a Construct or an Undead, it becomes infested with illithid tadpoles. While infested, the creature takes 16 (3d10) psychic damage at the start of each of its turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself after it succeeds on three of these saves. If the creature is targeted by magic that ends a curse or restores 40 hit points or more, the tadpoles infesting the creature are killed instantly, ending the effect on the creature. If a Humanoid is reduced to 0 hit points while infested, the creature is stable but remains unconscious for 6d12 hours. When the period of unconsciousness ends, the creature transforms into a mind flayer (see the Monster Manual) with all its hit points. Casting a wish spell on the unconscious creature rids it of the infestation and prevents it from turning into a mind flayer.

Legendary Actions.The creature can take 3 legendary actions...

Tentacle.The dragon makes one Tentacle attack.

Shatter Concentration (Costs 2 Actions).The dragon targets a creature it is grappling. The target's concentration on a spell it has cast or an ability it is maintaining ends, and the target takes 19 (3d12) psychic damage.

Elder Brain Dragon

One of the few consolations available to those who must contend with a mind flayer colony is the limit of its reach, which spreads only as far as the influence of the colony's elder brain. But this small solace withers away when a colony manages to capture a dragon. Teams of mind flayers bind the dragon, which is subject to a gruesome transformation as the elder brain latches onto the dragon's back and digs its tentacles into the dragon's brain. An elder brain dragon is the nightmarish result.

Using the mobility of the dragon's body, the elder brain can now serve as a powerful general to illithid armies, free from the confines of its brine pool. The elder brain dragon becomes a psychic threat in addition to a physical one, its body rife with aberrant influence and pulsing with psionic power. Even the elder brain dragon's breath weapon mutates during its transformation, becoming a stream of briny liquid roiling with illithid tadpoles. These tadpoles can swiftly slay victims and transform them into mind flayers, allowing the elder brain dragon to grow its own roving colony.