So you know how in the second battle with Tirek, he uses Blastwind to force one or two of your party members to be removed to make room for Twilight? I wanted to see what would happen if you manage to prevent any of your characters from being removed. Here was the result:

I am disappointed...

It seems to always replace the second party member by default.

Huh. That's interesting. Odd reaction on the game's part.