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Whosoever holds this hammer, if he be worthy, shall possess the power of Thor.
This statement suggests that when a worthy individual other than Thor wields Mjolnir, he would be granted the powers that Thor possesses. It seems reasonable to assume that Thor, when deemed worthy, shouldn't need Mjolnir to access the powers that innately belong to him.
We have witnessed a worthy Thor without Mjolnir existing while a worthy Vision wielding it was by his side. Using this as an example, what is the "power of Thor" that by definition both should simultaneously possess in that moment?