The Elder Brain

Your patron is a hive mind of the Ilithid race. Whether through accident or foolishness,
you have bound yourself to a being of pure Psychic force, whose will is absolute. Such a
pact makes your mind a literal force to be reckoned with, but at great risk. Will you
conquer the madness, or fall to the domination of the Elder Brain?

Hive Consciousness

At 1st level, the influence of the Elder Brain on your mind alters it, allowing you to communicate
telepathically with any creature that you can see within 120 feet of you. You may choose to communicate with language, images, or sheer emotion. The creature must be able to speak the language you choose to communicate with in order to understand you. 

Additionally, once per short rest, you may cast the Detect Thoughts spell without consuming a spell slot, and you gain the following Expanded Spell List:

Spell Level
1st – Tasha's Hideous Laughter, Sleep
2nd – Levitate, Phantasmal Force
3rd – Sending, Slow
4th – Confusion, Hallucinatory Terrain
5th – Telekinesis, Modify Memory

Finally, once per long rest, you may choose to open
your mind to the hive consciousness, requiring you to make a Charisma Saving Throw equal to your
spell save DC. Upon a success, the hive consciousness momentarily shares the burden of your thoughts,
giving you advantage on all concentration checks for one minute. Upon a failure, the hive
consciousness overwhelms you, subjecting you to Short Term Madness (DMG page 259).

Eldritch Synapse

Starting at 6th level, the Elder Brain deepens its connection to you, sharing ancient eldritch knowledge
at the cost of arcane energy. You may choose to expend a spell slot to gain an Eldritch Invocation of
your choice for a number of rounds equal to the level of the spell slot consumed. You must meet the
prerequisites of the Invocation in order to use it.

Mind Crank

Beginning at 10th level, your mind begins to forcefully draw on the power of the Elder Brain during
combat. You may choose to make your Eldritch Blast spell deal Psychic damage instead of Force
damage upon casting it. Additionally, a number of times per long rest equal to your Charisma Modifier
(Minimum 1), you may use a bonus action to empower your Eldritch Blast with the power of your
thoughts. The next targets struck by your Eldritch Blast spell must make a Wisdom saving throw equal
to the Warlock's spell save DC. Upon a failure, the Warlock may reroll any 1's and 2's during the
damage calculation of Psychic damage against the target for one minute.

Elder Arcanum

Upon reaching 14th level, your influence upon the Elder Brain has greatly expanded, allowing you to
draw upon its full power in momentary spurts of sheer will. When channeling this ability, you must
perform a DC 17 Charisma saving throw, or be dominated as per the Dominate Monster spell by the
Elder Brain for one hour. Upon a failure, the Warlock may attempt another saving throw every ten
minutes until the Elder Brain's hold on them is broken, and may not attempt to channel another
Elder Arcanum until the end of their next long rest. Upon a success, however, you may expend a
Mystic Arcanum spell slot to infuse an Eldritch Blast with one of the following abilities depending on the level of the spell
slot consumed.

Whispers of the Hive (6th Level) – Creatures struck by your next Eldritch Blast go mad for one minute.
For the duration, the Warlock may use their reaction to make the target or targets perform a basic melee
attack upon an enemy of the Warlock's choice. The enemy must be within melee range of the maddened
creature or creatures.

Mind Siphon (7th Level) – Enemies struck by your next Eldritch Blast have their thoughts torn from
them and transferred to you. You heal for an amount equal to the total damage dealt by your Eldritch
Blast, may read their minds as per the Detect Thoughts Spell, and you gain advantage on all Spell
Attack Rolls against the affected targets for one minute.

Traumatize (8th Level) – Your next Eldritch Blast has the power to shatter a mind, dealing an additional
12d6 Psychic damage to each target. Furthermore, each affected target receives a penalty to all attack
rolls, saving throws, and concentration checks equal to the Warlock's Charisma Modifier (Minimum 1)
for one minute.

Assimilate (9th Level) – Your will over the Elder Brain becomes absolute for a split moment, taking its
full Psychic might into your mind and directing it at your enemies. Each target struck by your next
Eldritch Blast are dominated for one minute as per the Dominate Person spell. After the effect ends, the
dominated targets are subjected to Indefinite Madness (DMG Page 260) and are charmed by you for the
next 24 hours. Creatures immune to the domination suffer 15d8 Psychic damage and are immediately
subjected to Long Term Madness (DMG Page 259).