That which does not kill...

 

The Illithids only had one weapon.

The Illithids only NEEDED one weapon.

The Illithids were known and feared throughout several galaxies for the irresistable power of their weapon.

They had evolved telepathy, and their method of killing prey was simple. They would form a telepathic link with the victim's mind, and send a psychic command for all neural activity to stop. There would be a moment's pause while the brain and nerves shut down, and then the victim would collapse, a lifeless husk. Then, the Illithids would feed.

World after world, species after species, had fallen to the Mind Flayer empire. No defense could be found. Species with metal skulls, species whose minds were distributed throughout their entire bodies, species with crystalline brains, species with weaponry that could vaporize any foe and shields that could repel any physical attack... all lay helpless before the Mind Flayer's one weapon. Planets and solar systems were abandoned in headlong flight when news of approaching Illithid ships came. 

Until they came to Terra.

The Hive Mother itself was aboard the ship that abducted the first intended human victim, reconnaissance having established that the humans had the most complex and therefore nutritious brains. Other similar carbon-based species from the same planet had easily been dispatched by the usual method, including other primates, and no meaningful resistance was anticipated. No meaningful resistance was possible. Hive Mother stood to its full height, slightly taller than the human female, forced the telepathic link as usual, and gave the usual command: DIE.

The human gasped, and then coll-

did NOT collapse as expected, but blinked twice, then grabbed a fistful of tentacles in each hand, lowered her head, and YANKED with such force that the Hive Mother's invertebrate brain was smashed to pulp against the human's forehead while several tentacles were torn from the Mind Flayer's face.

As the Hive Mother lay screeching and thrashing in its agonized death throes and the other Mind Flayers looked on in shock, to their horror they heard the human's thoughts enter THEIR minds. And as they turned to flee (too late, it would turn out) the last thing they heard was this:

"Bitch, I have depression, I ALWAYS have a voice in my head telling me to die. I have defied that voice for 20 years and I SURE as fuck will not obey now."