Pact of the Brain

Elder Brains are cunning, reclusive, and powerful leaders that lead their armies of Mindflayers into the world with unrelenting strength, never closing their all-seeing eye for any reason. These traits are the ones that Warlocks who pledge their allegiances to these monsters seek to embody. The idea that one might be able to surprise or sneak up on a Brain Warlock is one that can be met with laughter and scoffs. They are masters of perception and command and can even benefit from the Elder Brain's mindflayer servants.

Mindwatcher

At 1st level, you are given a Mindwatcher companion. A Mindwatcher is similar to a Mindwitness but far smaller and less powerful. It is designed to watch over you and was created by your Elder Brain patron. The Mindwatcher can understand any language you speak but cannot speak for itself. It is a tiny aberration. As a bonus action, you can summon your Mindwatcher within 5 feet of you. The Mindwatcher assists with whatever task you require for one minute, after which time it will portal back into your mind.

When you summon your Mindwatcher, it can make a ranged spell attack within 60 feet of it, shooting a ray of energy from its eye. When this occurs, roll 1d6 to know what the ray's effect will be: 1: The target must make a charisma saving throw each round at the start of its turn until it succeeds. On a failed save, its next attack has disadvantage. 2: The target must make a Wisdom saving throw each round at the start of its turn until it succeeds. On a failed save, it is frightened. 3: The target must make an Intelligence saving throw. On a failed save it takes xd4 psychic damage and half as much on a successful save, where x is your proficiency bonus. 4: The target must make a Dexterity saving throw every round at the start of its turn until it succeeds. On a failed save, the target's speed is halved. 5: The target must make a Strength saving throw or be grappled by the Mindwatcher's beam. 6: Nothing Happens.

As a bonus action, you can move the Mindwatcher up to 30 feet away from you.

You can summon your Mindwatcher once per short or long rest. You can summon it one additional time at 4th, 8th, and 16th level.

Aberrant Knowledge

At 1st level, you are able to telepathically communicate with any creature you can see within 60 feet of you. Additionally, you can speak, read, and write in Deep Speech if you cannot already. You are also proficient in perception.

Protected Mind

At 6th level, you gain resistance to psychic damage. Additionally, you can make a reaction when hit with a psychic damage attack, making an intelligence saving throw. On a successful save, the damage is reflected back at the attacker, dealing a d10 of psychic damage per half your warlock level. You can use this ability an amount of times equal to your proficiency bonus.

Brain Shield

At 10th level, you gain the ability to activate your mind shield as a bonus action. You must maintain focus to keep the shield up. When the mind shield is active, you are immune to psychic damage and all attack rolls have a disadvantage hitting you. When you are dealt damage, you can decide to take none and reflect it back onto the attacker. You can reflect damage a number of times equal to your Intelligence modifier.

Trusted Ally

At 14th level, you are at the highest rank a non-flayer can possibly be. You gain the ability to summon 1d4 Mindflayers on your turn as an action. They stay in your service under your command as long as you have focus. Otherwise, they transport themselves back to their lair. Additionally, Mindflayers automatically empathize with you and will not attack unless provoked.