Elder Brain, Variant (5e Creature)
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Huge aberration, lawful evil
Saving Throws Int +15, Wis +12, Cha +12
Magic Resistance. The elder brain has advantage on saving throws against spells and other magical effects.
Psychic Defense. While the elder brain is wearing no armor and wielding no shield, its AC includes its Wisdom modifier.
Innate Spellcasting (Psionics). The elder brain's innate spellcasting ability is Intelligence (save DC 24, +15 to hit with spell attacks). It can innately cast the following spells, requiring no components:
Multiattack. The elder brain makes two tentacle attacks.
Tentacle. Melee Weapon Attack: +8 to hit, reach 60 ft., one creature. Hit: 31 (4d10 + 9) psychic damage. If the target is Large or smaller it is grappled (escape DC 17) and must succeed on a DC 17 Intelligence saving throw or be stunned until the grapple ends. An elder brain has eight tentacles and each can grapple one creature.
Reel. The elder brain pulls each creature grappled by it up to 30 feet straight toward it.
Brain Consumption. Melee Weapon Attack: +8 to hit, reach 5 ft., one incapacitated humanoid grappled by the elder brain. Hit: The target takes 78 (12d12) piercing damage. If this damage reduces the target to 0 hit points, the elder brain kills the target by absorbing its brain and gains 20 temporary hit points.
Mind Blast (Recharge 5-6). The elder brain magically emits psychic energy in a 120-foot cone. Each creature in that area must succeed on a DC 17 Intelligence saving throw or take 45 (8d8 + 9) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
The elder brain can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The elder brain regains spent legendary actions at the start of its turn.
Tentacle. The elder brain makes one tentacle attack.
At center of a mind flayer colony rests the elder brain, a living well of immeasurable psychic might that seeks to further the illithid's domain over all creatures. These horrible creatures resemble a massive alien brain with eight thick tentacles about its form. Its underside is a writhing mass of smaller tendrils that probe at the world around it. While elder brains usually act as extensive mental libraries and advisers for their illithid underlings, they are more than capable of defending themselves.