Complex sentence: As she started to sing, more dancers joined in on smaller, circular platforms while fire shot from the floor and a long, rectangular screen merged video of flames with images of the performers, seemingly setting them on fire.
Split into simpler sentences: As she started to sing, more dancers joined in on smaller and circular platforms. Simultaneously, fire shot from the floor and a long, rectangular screen merged video of flames with images of the performers, seemingly setting them on fire.