^First no one had Mastered Super Sayin. The only 2 who ever do that is Goku and Gohan and since Goku and Gohan were not super syain the whole Movie we can saflty say they are not masters of Super Syain.
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LegendarySSj7 would say the movie time line is different than the real DBZ time line and that the Brolly Movie happens around the time (in the real DBZ timeline) that Gohan and Goku were in the time chamber and Gohan was Super Syain but still had not mastered it.