 When mama introduces Billy Flynn for the first time, the "All I Care  About is Love" dancers slowly appear behind her. There were no CGI  effects involved, it was simply a scrim. In fact, the only CGI  effects throughout the movie are from "erasing" the harnesses on  Christine Baranski (qv) (Mary Sunshine) and on some of the  reporters during the end of the "We Both Reached for the Gun"  number.