If you guys remember that episode where Mayor Dewey had Steven and Jamie put on a play, and Pearl reworked the script to be accurate, there was a massive fusion that warned Dewey about the dangers of Beach City. My guess is that particular fusion is the one between Garnet and Rose, or Garnet, Rose, and Pearl. Due to Garnet's size, and Rose's size, I think that it could have been the two of them.