Could it be? (mystery man over Sasuke)
Re-reading the most recent couple chapters, i stumbled across this
In the middle-right panel, you see i believe Madara saying "Those on the verge of death require on-field treatment"(Sasuke?)
Then there's a white Zetsu saying "i'll head out immediately!"
Could it be that the mystery person by Sasuke is just a Zetsu, going there to treat him on Madara's orders? Why would Madara even want to save Sasuke? Or anyone for that matter? That selfish prick seems to only care about himself, but he may have uses for Sasuke...
I would be disappointed if Kishi has been trolling us with this Mystery person and it's just a white Zetsu sent by Madara...
UPDATE: Okay so it seems Madara is probably just talking about the infinite tsukiyomi plan here. Credit to DRAW for pointing it out.
Another thing came to mind recently.
Hashirama gave Sasuke a jutsu right before he went to go fight Madara. Is there a possibility that maybe this jutsu is the reason why the "mystery person" whose chakra Karin does not recognize appeared? I myself find this hard to believe so bare with me. Hashirama said it was a jutsu that would bind Madara in response to him taking his Senjutsu chakra.
We've yet to see what exactly it is as Sasuke got owned pretty quickly, but at this point it could be anything, even a technique that would summon someone in response to Sasuke being mortally wounded, you never know.
Another thing to keep in mind is that whoever it is, Tobirama does not recognize them....http://narutobase.net/manga/Naruto/664/2
I could go on, I might add more later. Honestly not sure who it's going to be at this point, but I'm looking for hints in previous chapters....that's enough of my ranting about nothing heh