Your Intelligence score increases by 2, and your Charisma score increases by 1.

While colonial illithids are always lawful evil, as they are under the control of an arrogant and domineering elder brain, renegade illithids can be almost any alignment. Good illithids are extremely rare however, as their intrinsic nature requires them to kill others and feast on their brains in order to nourish themselves and survive.

Illithids fully complete ceremorphosis not long after the tadpole is inserted, and become fully mature after a few more years. It is known that illithids live longer than humans, but their maximum age range is not known.

Most illithids are at least as tall as larger humans, standing at minimum a few inches under 6-feet. Their bodies are very slender, weighing much less than an average being of their stature. Your size is Medium.

Your base walking speed is 30 feet.

Your creature type is aberration, not humanoid, and you are affected as such by spells and other effects.

Your innate spellcasting ability is Intelligence. You can innately cast the following spells at will, requiring no components; detect thoughts and levitate. Once you reach 11th level you can cast plane shift once per long rest, targeting only yourself, without expending a spell slot or requiring components. At 13th level you can cast dominate monster once per long rest without expending a spell slot or requiring components.

Tentacles

Your tentacles are natural weapons. Intelligence is your attack bonus and damage bonus, and the reach is 5 ft. On a hit, it deals 1d10 + your Intelligence modifier in psychic damage. Once you reach 3rd level, the target must succeed on a Strength saving throw DC 8 + your Intelligence modifier + your Proficiency bonus or be grappled, and you cannot target another creature with your tentacles without ending the grapple. They can repeat the saving throw at the beginning of each of their turns, ending the effect on a success. The target must also succeed on an Intelligence saving throw DC 8 + your Intelligence modifier + your Proficiency bonus or be stunned until the grapple ends. They can repeat the saving throw at the beginning of each of their turns, ending the effect on a success. The damage increases by 1d10 when you reach 5th level (to 2d10).

Extract Brain

As an action, you can attempt to devour the brain of an incapacitated creature that is grappled by you, dealing 1d10 + your Intelligence modifier in piercing damage and 1d6 psychic damage. If this damage reduces the target to 0 hit points then you devour their brain completely and gain temporary hit points equal to your level + your Proficiency bonus. In addition, you may receive all the knowledge and memories that the consumed brain had, as well as intimate knowledge of their personality. This creature must be size Large or smaller. Alternatively, you may consume the brain of a creature that has died within the last minute and gain the same benefits. The piercing damage dealt increases by 1d10 at 5th level, and again at 10th and 15th level.

Mind Blast

You can magically emit psychic energy in a 60-foot cone. Each creature in that area must succeed on a saving throw DC 8 + your Intelligence + your Proficiency bonus or take 1d8 psychic damage and be stunned for 1 minute. A creature takes half as much damage and isn't stunned on a successful save. It can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. The damage increases to 2d8 at 5th level, 3d8 at 10th level, and 4d8 at 15th level. After using your mind blast, roll a d6 at the beginning of your next turn; if the result is a 5 or 6 the ability recharges and you may use mind blast again that turn, if not then roll again at the beginning of the turn after. Additionally, this ability automatically recharges at the end of a short or long rest.

Darkvision

Accustomed to the Underdark, your eyes can easily make out details in low-to-no light conditions. You have darkvision out to a range of 120-feet. You can see in dim light as if it were bright light and darkness as if it were dim light, but you cannot perceive color in darkness, only shades of grey.

You have advantage on saving throws against spells and other magical effects.

When you reach 6th level, you gain the ability to imbue a sword with psychic energy, turning it into a mind blade that deals an additional 2d6 psychic damage on top of the items base damage. Only you or a creature charmed by you may attune to and use the mind blade. In anyone else's hands, the mind blade functions as a nonmagical weapon of the same type. You must be in physical contact with the weapon for the duration of a long rest and if the rest is not completed then the imbuing fails, destroying the item being converted.

You can communicate mentally with other creatures within a 120-foot radius. The creatures don't need to share a language with you but must know at least one language, or be telepathic themselves, for telepathic communication to function. A creature without telepathy can receive and respond to telepathic messages but can't initiate or terminate a telepathic conversation.

You can speak, read, and write Undercommon and Deep Speech. Undercommon is a language of commerce among the subterranean races in the same way Common is among the surface dwellers, and Deep Speech is the language of Aberrations.