Mind Flayers

Sometime before recorded history, mind flayers entered this plane from another, stranger dimension. They have psionic powers that enable them to control the minds of other creatures, and they can communicate telepathically. Most mind flayers are workers living in hives and serving the commands of their "queen", the Elder Brain. ("Queen" is used only by analogy to hive insects like bees and ants; mind flayers reproduce asexually, and many have no conception of gender as anything other than a different "flavor" in your delicious, delicious brains.) The mind flayers in a hive work together to strengthen the hive and bring food (brains) to the queen.

Basic Information

Genetics and Reproduction

Mind flayers reproduce by laying eggs that hatch into tadpole-like creatures, which then invade a humanoid's cranium, usually after the humanoid has been rendered unconscious by the powers of an adult mind flayer. The tadpole attaches to the brain stem and proceeds to devour the humanoid's brain. Over the course of a week, the humanoid's body changes, eventually becoming the mind flayer we all know and recognize. The mind flayer might retain memories or personality quirks from its previous life as a (non-brain-eating) humanoid, but these recollections do not seem to have any impact on their new, brain-eating lifestyle.

Growth Rate & Stages

Tadpoles that survive for more than a few weeks without consuming a humanoid continue to grow, and, like adult mind flayers, they survive by consuming psychic energies (including, but not limited to, humanoid brains). Hives will cull tadpoles before they grow too large, and the gith warn of the consequences of eliminating a mind flayer hive without paying careful attention to the extermination of the tadpole pool.

Dietary Needs and Habits

Mind flayers subsist on the brains of humanoids, and must consume at least one brain per month to survive. When they devour a humanoid's brain, they learn everything there is to know about that person (that the person themself knew) - their memories, personality, interests, and innermost fears are part of a varied and balanced diet.

Biological Cycle

As a mind flayer hive grows particularly large, it becomes more likely that a new mind flayer "born" into the colony will be exceptionally psionically powerful. These "queen-candidates" leave the hive, taking a substantial portion of the existing workers with them, and travel hundreds of miles away. There, the workers create a refuge, and - through processes not fully understood - the queen-candidate metamorphoses into an elder brain queen and forms a new hive.

Additional Information

Perception and Sensory Capabilities

Mind flayers communicate with each other - and with other creatures - using telepathy. A hive of mind flayers is psionically linked into one large information network, and the instant a worker learns something new, they transmit it to all the other members of their hive. New mind flayers who join the hive gain all the memories of every previous worker in the hive.
This "hive mind" seems to only work for mind flayers that are within 5 miles of their brain-queen. Beyond that distance, it is possible to separate a mind flayer from the knowledge and expertise of the rest of its hive.

Symbiotic and Parasitic organisms

A mind flayer hive working in concert can parasitically infect a humanoid's psyche, removing the individual's original wants and desires and replacing them with the hive's own. This thrall can then communicate telepathically with the hive that created it, as if it was itself a mind flayer. The gith report that this process takes at least a week, and requires a great deal of effort from the hive. It is an arduous process to return these thralls to their former selves, but it can be done.

Civilization and Culture

History

A mind flayer empire once dominated the Astral Plane. It is widely believed that the gith destroyed all the edifices that the mind flayers created during their rebellion (see The History of the Gith), but some believe that mind flayer ruins - or perhaps even active hives - still exist somewhere in that endless space.

Sentient

Yes

Diet

Your brains