The Illithid

The Illithid patron is a powerful entity among the ranks of the mind flayers. Obsessed with enhancing the hivemind's collective knowledge, the Illithid has expanded its influence to include adventurers who know not better.

The Illithid could be a particularly influential mind flayer, an elder brain with uncharacteristically long reach, or the god Ilsensine itself.

Expanded Spell List

The Illithid lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

 

Illithid Expanded Spells

Spell Level	Spells
1st	inflict wounds, dissonant whispers
2nd	tasha's mind whip, nystul's magic aura
3rd	slow, glyph of warding
4th	confusion, evard's black tentacles
5th	wall of force, dominate person

Expanded Mind

When you take this subclass at 1st level, your patron grants you the ability to weaponize your knowledge. Your spellcasting modifier for the Warlock class becomes Intelligence.

Elder Influence

Starting at 6th level, your intellect begins to influence those around you. You can telepathically communicate with creatures within 30 ft. of you, whether you can see them or not. A creature communicated with in this way does not know the origin of the telepathy unless you allow it to, or if it makes an Intelligence(Arcana) check against your spell save DC.

If a creature can telepathically hear you but does not know the origin of this telepathy, you can use an action to force it to make an Intelligence saving throw, taking 6d8 psychic damage and becoming stunned until the end of its next turn on a failed save. If it succeeds on the save, it takes half damage and is not stunned. 

You can use this feature once per long rest, or by expending a Warlock spell slot.

This damage increases to 8d8 and can affect a number of targets of your choice, equal to your proficiency bonus when you reach 10th level. At 14th level, the damage increases to 14d8.

Steeled Conscience

Starting at 10th level, you learn to shield your mind from those who would harm it. You become resistant to psychic damage and gain proficiency in Intelligence saving throws.

Borrowed Knowledge

You can spend 1 minute to consume the brain of a creature that has died wthin 24 hours to heal yourself by 2d8 hit points. When you do so, you can learn the rudimentary details of its life, such as the creature's name and and origin. The fresher the brain is, the more information can be extrapolated from it.

If the creature has an Intelligence score of 5 or lower, you learn nothing and instead take 2d8 points of poison damage.

Hivemind

At 14th level, your hunger for knowlege manifests itself. As an action, you can alter the corpse of 1 humanoid or aberration within 30 feet of you, turning it into an intellect devourer with an Intelligence score equal to yours (adjust stats and saves accordingly). You can command it to take its turn immediately after yours (no action required).