Deception and Persuasion checks are rolled with disadvantage, and Intimidation checks are rolled with advantage.

Nearly all Illithid are never seen without at least two thralls, and develop intimate connections with them – mourning their deaths, and even going mad from loneliness without a companion. As long as you can see at least two allies within 30ft, you have advantage on saving throws to avoid being Frightened, and disadvantage on those saving throws if you cannot see any.

Your Intelligence increases by 2, but your Charisma decreases by 2.

You count as one size larger when determining your carrying capacity and the weight you can push, drag, or lift.

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. You can't discern color in darkness, only shades of gray. 
You have disadvantage on attack rolls and on Wisdom (Perception) checks that rely on sight when you, the target of your attack, or whatever you are trying to perceive is in direct sunlight.

Talk to your DM if your Illithid has acclimated to the surface long enough to adjust to the amount of light. If so, you lose Sunlight Sensitivity and your Darkvision range decreases to 60ft

You speak Deep Speech, Undercommon, and have a Telepathy range of 60ft.

You know the Minor Illusion cantrip. You can also cast Mage Armor at will.
Starting at 3rd level, you can cast the Charm Person spell with this trait.
Starting at 5th level, you can cast Invisibility with this trait. You can also cast Misty Step with this trait.

Once you cast Charm Person or Invisibility with this trait, you can't cast that spell with it again until you finish a short rest. Once you cast Misty Step with this trait, you can't cast that spell again until you finish a long rest. You can also cast any of these spells using any spell slots you have of the appropriate level.

Intelligence is your spellcasting ability for these spells when you cast them with this trait. None of these spells require spell components when you cast them with this trait. In addition, you use your Intelligence modifier when setting the saving throw DC for the spell you cast and when making an attack roll with one.

Spell save DC = 8 + Proficiency Bonus + Intelligence Modifier
Spell attack modifier = Proficiency Bonus + Intelligence Modifier

You can use your Action to Grapple a creature and use your Bonus Action to drain their mental energy. The creature makes a DC Intelligence save or takes 1D10 plus your Proficiency bonus in psychic damage, and you gain temporary hit points equal to half the amount of psychic damage dealt. Any target that is incapacitated automatically fails. If Devour Mind reduces a target’s Hit Points to 0, the target is killed.

As an Action, you can emit psychic energy in a 60ft cone. Each creature in that area must succeed a DC Intelligence save or take 1D8 plus your Proficiency bonus in psychic damage and be stunned until the end of your next turn. Affected creatures can repeat the saving throw at the end of each of their turns, ending the effect on themselves on a success. You can repeat this ability a number of times equal to your Proficiency bonus before requiring a long rest.