As insane as it might sound, could this fanfic Madara possibly beat Kaguya? Kamui is an incredibly useful asset against Kaguya seen in the manga on multiple occasions. Intangibility trolls dimension shift so no getting killed by acid, encased in a block of ice, falling into lava etc. Madara can travel through dimensions if he needs to
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and the fact that Madara can create clones with shared vision due to Rinnegan could mean he can keep an eye out in other dimensions and know which one Kaguya moves to. Naruto already tricked her by leaving his shadow clones in another dimension and switching his Gudo Dama to a clone, something Madara can replicate with Limbo or Mokuton bunshin.
As for Kaguya's arsenal, it can be all be countered.
-Ash Bones can be
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, or
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away with kamui or
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.
-If Madara can corner her with clones like Naruto did, Kaguya's portals can be
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if she tries to exit dimensions and then he can nail her with his next attack (maybe a super close range kamui snipe? With DMS he can snipe and remain intangible at the same time.)
-Eighty Gods Vacuum attack can be repelled with Shinra Tensei...maybe. If not, there's always kamui.
-Giant TSB is phased through. Trololololol.
If this Madara is > VOTE Naruto and Sasuke, who already beat Kaguya without their strongest moves, maybe Madara can as well. Btw I'm talking about the version of Kaguya prior to just obtaining a massive amount of chakra from the IT.