This mod introduces Quayle from BG1 as a party joinable NPC. But the condition is ... Aerie's death. A mini quest (including a small new area) is provided, where you decide who you prefer to travel with. The mod includes time-triggered and scenery talks for both SoA and ToB, banters, interjections, and new items.
You need to unzip the mod and insert it into the BGII - SOA Game Folder. Start the Setup-Quayle.exe file and proceed with the instructions.
Since version 7.0 you may also install PIDs, but they are rather minimalistic. They were created in case all your other NPCs had some so Quayle won't stand out technically, but they do not add meaningful information and are more like a small addition to the mod's main component.
GAMES: BG2, BG2EE, EET