Complex sentence: Stephanie, Sportacus, and Robbie were the only human characters until episode 32 ("Dancing Duel"), the first to include Rottenella, played by Mauriello's stunt double, Kristjana Ólafsdóttir.
Split into simpler sentences: Stephanie, Sportacus, and Robbie were the only human characters on the show until episode 32 ("Dancing Duel"), which was the first to include a fourth live actor to play the role of Rottenella. She was played by Mauriello's stunt double, Kristjana Ólafsdóttir.