With Firkragg all you have to do to beat him is use brute force and healing potions(I beat him with 13th level party of monk,minsc,keldorn,jaheira,nalia,and aerie by just bumrushing him)
but with kangaxx most people have said they just exploit the a.i. or use cheap tricks. I fought kangaxx with the same party(now 16th level) and got my ass handed to me 11 times in a row because of that damn imprisonment.
p.s. When I finnally beat him I actually jumped up from my desk and yelled "yah ■■■■ you skull!" Lucky no one else was home at the time
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RULE #1:I am always right
RULE #2:See rule #1