Board Thread:Versus Debates/@comment-26958911-20151010214426/@comment-26636534-20160113123756

^Actually, he encountered the black flames after Itachi used it to break out of his jutsu(Which he investigated) and sealed it, I think if he sealed it for study then he would have gained a lot of info on it don't you? Also Jiraiya knew from level of mental damage Kakashi/Sasuke sustained from Tsukuyomi that he needed to find Tsunade to heal them, thus he knows about two of Itachi's MS powers and it's effects.

P.S. I said encountered not countered