Hi Seenco! Welcome to the forum! 
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Theorically, all is possible in dreams. The problem comes generally when you doubt about it. If you experience such problems, you often have to trick your dream, transforming an object in another for instance, or finding it in your pocket, etc. About fireballs, you perhaps could try to yell “Kamehameha!” like Sangoku…
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Another lenghtening technique is looking at your hands from time to time. If your dreams fades or you lose visuals, rub your hands.
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I don’t know. You perhaps will find some answers in this thread: Sex, kissing, etc. in dreams