While I agree with the cautions above about escalating matters into an arm's race, if you want to fight fire with fire, may as well go all the way.
Which, to me, means keep the Kuo-Toans exactly as they are, except that they have a full and perfect knowledge of all of the abilities and traits of the PC's. They know which spells the PC's carry, what magic items they own, their standard tactics, which of their saves are strong and weak, and they use this knowledge to have the perfect counter-tactics. PC's are loaded up on Acid spells? All the enemies are resistant to Acid (just like, and to the same extent, the PC's are resistant to electricity knowing that's a Kuo-Toan strength). Maybe only the one PC is so well-known.
How did the Kuo-Toans get all that incredible intel? Why, from the same methods the PC used!
Which, to me, means keep the Kuo-Toans exactly as they are, except that they have a full and perfect knowledge of all of the abilities and traits of the PC's. They know which spells the PC's carry, what magic items they own, their standard tactics, which of their saves are strong and weak, and they use this knowledge to have the perfect counter-tactics. PC's are loaded up on Acid spells? All the enemies are resistant to Acid (just like, and to the same extent, the PC's are resistant to electricity knowing that's a Kuo-Toan strength). Maybe only the one PC is so well-known.
How did the Kuo-Toans get all that incredible intel? Why, from the same methods the PC used!
