Board Thread:Theories and Speculation/@comment-5273810-20150207055437/@comment-5547501-20150409110949

What do you mean by 'Forbidden Three'? If you're talking about Amaterasu, Tsukuyomi and Susano'o, only Itachi had the first two and Sasuke had Amaterasu (due to their being siblings I assume). Every mangekyo has different powers, Obito's powers being the two variations of Kamui, one for each eye. If he had both eyes he might have used Susano'o then but he didn't so he couldn't.

Also, though it was only stated once and not focused on at all, Kakashi was actually going blind from the mangekyo and he used it far less than Obito did.