Within a 120 foot range, a creature with darkvision can see in darkness as if the darkness were dim light, so areas of darkness are only lightly obscured. 

You can speak, read, and write Common and Undercommon. In addition, you can write Qualith.

Generally lawful evil.

As a bonus action you can attempt to grapple a humanoid of Small or Medium size within 5 feet of you. The target must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check, DC 8+ your proficiency bonus + your Intelligence Modifier. On a success, the target breaks free of the grapple; on a fail the target is grappled and takes 1d6 psychic damage. You have advantage on attack rolls against the grappled creature. The target may repeat this check once on each of their turns except the turn they were grappled.

Mind Flayers live longer than humans, usually to 120 years but rarely past 150.

Most stand a few inches over 6 feet. Your size is Medium.

Your base walking speed is 30 feet.

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

As an action on your turn you can target a large amount of psionic energy at a creature you can see within 120 feet of you. The target must succeed on an Intelligence saving throw, DC 8 + your Intelligence modifier + your proficiency bonus or take 1d10 psychic damage on a failed save. You need to take a short or long rest before using this trait again.

At Higher Levels: At 3rd level this damage increases to 2d10. At 7th level it stuns the target for 1 round. At 11th level the damage increases to 3d10 and can target up to three creatures. At 15th level you can use this trait up to 3 times before you need to take a long or short rest.

While conscious, you may communicate telepathically with any one creature you can see within 120 feet of you, you do not need to share a language.

Instead of consuming 1 pound of food per day, an Illithid must consume at least 1 brain per month for nourishment. The brain must be from a size Small or Medium creature and has to have died within 1 minute. Consuming a brain of such a creature gives you access to 1 piece of lore the creature knew (or to the DM's discretion- 1 language) and you heal 1d10 hit points, this cannot exceed you hit point maximum.

If a creature drops to 0 hit points while you are grappling them using tentacle, you may use your reaction to break the skull of the creature and extract their brain, killing the creature. You can consume the brain of the creature immediately after extracting the brain (healing 1d10 hit points which cannot exceed you hit point maximum). You regain use of this trait after you complete a short or long rest.

At Higher Levels:  At 5th level, consuming brains this way heals 3d10 hit points and you regain one hit die or 3rd level spell slot (If you have the ability to use 3rd level spell slots). At 10th level, you can use Extract Brain as an action against a creature you have grappled, and if you do, that creature takes 5d10 piercing damage.