Maybe it's some kind of 'gun barrel': he can "rotate" it and another eye (Sharingan, whatever) comes in its place. This way he has access to several Sharingan eye powers.
Then again, I don't think I ever saw a chapter where Tobi uses different Sharingan eye techniques. So probably not, but it's an interesting idea.
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Last edited by Darkelve; August 21, 2012 at 06:49 AM.
Kakashi only said that in some area it is superior to the Sharingan.
But it's an interesting question what is in the left part of his face. At least on this we don't see anything strange:
Last edited by Fox666; August 21, 2012 at 12:00 PM.