[Blackbeard D. Kuma]

Joker turning out to be Doflamingo is not a surprise, however Vergo being his most trusted subordinate and the "mole" of the G5 marines is quite the revelation.

Of course, seeing as how Law also used to serve under Doflamingo, that would logically mean that he knows a lot about his "ability". That's going to be pivotal information on how to stop/defeat Doflamingo. All the more reason for Luffy to have Law as an ally.