User blog comment:Uraharattack/Question on Page 16 Chapter 225 - Blackbeard Theory/@comment-31516508-20180202071855

BB wielding both the Yami Yami and the Gura Gura stems from some kind of ability to "steal" DFs. Now we know this ability itself cannot stem from a DF, because we see Burgess in Dressrosa attempting to steal Luffy's fruit. We know Burgess didn't have a DF at the time of Corrida Colesseum because he was knocked into the water and was fine. I can't explain how BB himself is able to wield multiple DFs but I am inclined to say it has nothing to do with a DF because he can obviously teach it to his subordinates.