Your intelligence increases by 2 and your charisma increases by one 

Mind flayers are usually created by introducing a parasitic illithid tadpole into a humanoid host. Mind flayers can live around 125 years 

mind flayers are comparable in size to humans, although slightly thinner. your size is medium 

You are an aberration and a humanoid. Anything that would effect either creature type affects you

You have darkvison out to a range of 120ft

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. 

As a mind flayer you can use Psionics. at 3rd level you learn the detect thoughts, and levitate spell. and can cast them each once per long rest without using a spell slot. inteligence is your spellcasting ability for these spells. you may also  additionally cast these spells using a spell slot if you have them.

You can use an action to blast psionic energy in a 15t cone. Each creature in the cone must succeed on a intelligence saving throw with a DC equal to 8+you proficiency bonus if your INT modifier. on a fail a creature takes psychic damage equal to a number of d6's equal to your proficiency bonus. if a creature failed by 5 or more, they are incapacitated until the end of your next turn. 

once you use this feature, you cant again until you finish a long rest