Drink potion of intelligence to rise it to 25. Chaotic command is good but what I learned about Mind flayers and others big creature like this one, It is not always good to fight. Cast inv 10 radius over all tour party and try to sneek out wihtout fighting all of them. Improved Inv reduce their thac0 by 4 after you'r first move while inv. mirror image/ blur/ invisibility are all good spell to make a defense against their eat-brain attack.
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Maybe it's because I hate drows more than I hate Humans - Jarlaxle to Entreri