Complex sentence: During the extended results show there are usually group performances and/or special musical guests, up until the eponymous announcement of the winner of the series which is followed by an encore of the winner's single which sometimes includes pyrotechnics/fireworks.
Split into simpler sentences: During the extended results show, there are usually group performances and/or special musical guests. When that happens, he or she will perform an encore of the winner's single which sometimes includes pyrotechnics/fireworks.