Increase the Immortal build limit trick (Fu Xi)
Save the game and quit in Archaic, Classical or Heroic age and your Immortal build limit (8) will increase by 2 with every age advance. A negative side effect: Archaic - Classical save disables both Fire Lances and Sitting Tigers, Heroic save disables Sitting Tigers. Immortal limit can't be increased for Nu Wa and Shennong, but they also lose their access to siege weapons because of saving the game. Archaic save for Nu wa also means, that she can't build Market in Classical age.