You know the creature is a Mind Flayer. It is known to attach its tentacle and control the victim's brain.
It's a mind flayer, a devastating beast that attacks with it's tentacles and mind. The tentacles can grapple and once attached does intelligence damage. furthermore, an even more vicious attack is it's ability to project out 60 feet a psychic static that stuns people, which is convenient so it can then use it's tentacles to suck the intelligence out of it's victims. Mind flyers also have a few spell like abilities that are mental in nature.