OK. I know this has been talked to death, but I'm in the Underdark, and HEIGHT ADVANTAGE HAS TO GO!!!!
It's utterly ridiculous. Kuo-Toa archers up on the rocks firing at my characters with max armor and shields and Shield of Faith enabled with an AC of like 21 or 22, and they're pegging me with Critical Hits every two seconds? Why? Because they can roll two d20s every time they shoot, increasing their chances of a Critical Hit every shot. I must have gotten hit like a dozen times in that one battle with a Critical Hit from those archers. It was ridiculous. And then, I'm trying to shoot them, and I kept missing like a noob because I had disadvantage because they were on higher ground.
Ugh! It was frustrating fight. Most of my party was almost dead by the time it was over, and it was MOSTLY because of the archers. It wasn't because of Boooal or the Kuo Toa high priest or anything like that. Nope. It was the dumb archers on high ground.