When ur in the underdark and u go to the mindflayer dungeon and later get near getting out but then u have to kill the flayers i cant figure out how to kill them i use the brine potion when ready to fight but after a min they kill me iv tried multible times even used the shadowkeeper to make my party like gods but i still doesnt work what am i doing wrong???????????

First of all, welcome to IW, mindflayer drain intelligence, so fighters with low intelligence die very fast, a good tactic is to summmon some skeleton warriors(lvl 3 or 4 cleric spell and lvl 5 mage spell i think, not sure though) or some mordenkainens swords, lvl 7 mage spell, which are excellent for killing mind flayers, hope i could help

Or you can also use the Potion of Genius which will temporarily raise your intelligence up to 25 or there is also the Psion Sword but thats on TOB if you have that installed. It protects you against mental mind attacks.

In my experience it´s sufficient to use Chaotic Commands on your fighters making them immune to their psionics. If your fighters don the drow armours and shields yous hould have found by now they should have an AC of about -10. With an AC that low *normal* Illithids very rarely hit you - if they hit just run away and wait until the effect wears off (very short duration).
With Ulitharids just play a little hit-and-run game ...

Using this tactics it was no problem for me to take on 3-4 Illithids at a time together with their hulk buddies.