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

You can speak telepathically with any intelligent creature within 120 feet.

You have the ability to avoid psychic detection and can extend that protection to those around you (similar to a pass without trace spell, but the ability in no way masks physical detection). 

For the duration (1 hr), each creature you choose within 30 feet (including you) cannot be tracked by psionic or magical means unless you fail an Intelligence saving throw at +5 for passive searches (general scans) and +2 for active searches (an entity specifically searching for you and/or those with you). 

You innately know these psionic powers: Mage Hand cantrip (mage hand is invisible). At 3rd level, you can manifest Mental Barrier (Shield ) and Detect Thoughts. When you reach 5th level, you can manifest the command and Levitate power. At 10th level, you can manifest the Dominate monster and Telekinesis power. When you reach 18th level, you can manifest plane shift (self only). These powers require psi points  as any other.

Intelligence is your spellcasting ability for these powers and your save DC equals 8 + your proficiency + your intelligence modifier. 

Using a focused wave of mental energy, you have the special ability to stun opponents, dealing 2d6 psychic damage to all within a 60 foot cone.

When you use your mind blast, each creature in the area of the blast must make a Intelligence saving throw.

The DC for this saving throw equals 8 + your Intelligence modifier + your proficiency bonus.

A creature takes 2d6 damage on a failed save and is stunned for 1d4 rounds or until making a saving throw at the end of their turn.

They receive half as much damage on a successful save and are not stunned. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level.

After you use your mind blast, you can’t use it again until you complete a long rest.

When you consume the brain of a recently deceased (within 1hr) creature, you can learn one piece of information it knew. Roll an Investigation check, and on a success, you learn what you want to know if the creature knew it. If the creature was intelligent (5 or higher) you also gain 1 psi point per level (or hit die) up to your maximum. You cannot exceed your maximum psi points in this manner. 

Your psychic abilities are dependent on the regular consumption of neural matter. One brain of intelligence of 5 or more or 10 of intelligence 5 or less will provide neural sustenance (and full powers) for a month. After a month without this minimum level met, you will lose 1 psychic ability and 1d4 hitpoints per week. After 2 months without this minimum met, you will fall into a catatonic state and will not awaken unless force fed neural matter. 

You can consume other food, though it will not meet the requirements to maintain your psychic health. The neural matter is enough to sustain you both physically and mentally. You require the same amount of water your host did. 

Your great psychic power has dulled some of your other senses. You have no sense of smell and a limited traditional sense of taste. 

You are alien to both illithids and non-illithids. You suffer disadvantage on all Wisdom (Insight) checks with non-aberrations, even if you are proficient in them, and on any Charisma ability score checks in which you are not proficient.

Your natural lifespan is 150-250 years. In that time, your physical form will remain that of the host at the time of attempted ceremorphosis. Injury and exposure to elements may alter your appearance, but age alone will not.

Illithids have an innate tendency towards evil, domination and order. This is mainly due to the influence of an elder brain that bands all Illithids within 5 miles of it under a single consciousness. Semi-ceremorphs are often more able to resist this, and can often use their unique psychic camouflage ability to exist on the fringes of illithid society without being noticed, even by the powerful abilities of an elder brain. Semi-ceremorphs tend toward lawful evil alignment like their illithid creators, though neutral and even chaotic individuals are not unknown. Given their primal urges and unique dietary needs, it is difficult for semi-ceremorphs to be truly good. 

You can speak, read, and write Deep Speech, Undercommon and, unlike most non-illithids, can manage to read Qualith (the Illithid way of writing that can only be read through touch) with your fingers. You can also write in qualith, if you have a striator (illithid writing device).  

Your illithid heritage imbues particular manifestations of psionic displays. The most evident is an increased amount of ectoplasmic seepage from the Ethereal plane when utilizing psionic powers. Unless suppressed (concentration check), your skin and hair (if present) is dampened with ectoplasmic residue. This will evaporate relatively quickly, and has no adverse effects.

Illithids are born in darkness and live in the darkest corners of the world; you have superior vision in dark and dim conditions. You can see in dim light within 120 feet of you as if it were bright light, and in darkness as if it were dim light.