It was, in fact, a series of well-positioned sunbursts. Other spell highlights included Agar's maximized polar ray, a nice cone of cold from Ioun, a maximized flame strike from Velendo, a ray of enfeeblement from Agar (which was ineffective, due to a well-considered spell immunity on Caustas), and several additional bits of glorious mayhem. An exact round-by-round accounting would have forced me to compare Caustas's potential to his ugly ugly death, and would have just made me cry even harder. *sniff*
For folks not in my game, his stats have been posted on the thread-which-must-not-be-named.
Man, I thought it was so clever having a runty cloud giant with almost full cover serving as the Imperator's healing battery. Thanks to Fajitas (who played Ioun, while WisdomLikeSilence played Annel) and the maze spell, it turned out to be a lot less efficacious than I had expected.