Doctor Strange: Multiverse Of Madness - Doctor Strange's dark dimension magic theory
Audience were confused by seeing that how Doctor Strange was controlling mirror dimension in Spider-man: No Way Home. Is he started too, of using dark dimension magic like ancient one for controlling mirror dimension.
Mirror dimension doesn't work as you think. Creator of mirror dimension can change its rules and class without any dark dimension magic they are the only one who can control mirror dimension and the prof is Doctor Strange movie's scene where ancient one is introducing mirror dimension to Doctor Strange for the first time.
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At that time ancient one was using mirror dimension without any external source. So the question is what is the use of dark dimension magic in mirror dimension?
Dark dimension magic in mirror dimension is used for accessing control of mirror dimension, from its creator. If you remember the fight between Doctor Strange and kaecilius, at that scene Strange cast the mirror dimension, but kaecilius takes authority from Strange. Condition becomes very different, mirror dimension was belong to Strange but kaecilius was using it, at that time he was using magic from dark dimesion.
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At the same scene where Kaicilius fight with Ancient One, scene become very different. Ancient One reversed every thing and takes the authority from Kaecilius. At that time she was using magic from dark dimesion.
So, mirror dimension can be used without any magic form dark dimension. This conclude that Doctor Strange was not using any magic from dark dimension in No Way Home.