If Madara gained Rin'negan and part of Hashirama's strenght just before his death,and he knows about Tobi he could easily use his yinn chakra and use yang chakra to create a body(Tobi) and give him life! So tobi would be just a part of Madara's chakra! It is possible look for my proof:
Dont say im crazyyy?!?!
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Dont say im crazyyy?!?!