A few weeks ago, I guess that Punk Hazard is the island where Akainu and Aokiji fight in, and in this week, Oda prove that what I guess was true. Actually world goverment has blockade this island
four years ago. Because it is used to be an experiment island for Doctor Vegapunk, seems that he was failed here and some posion gas was leaked.
I think someone just take full use of this island and want to implement their project at this desert island, the secret "M". He or she is the secret leader of this island and maybe he is also one of the Shichibukai from waht the "leg" said. After escape from the prision, Sanji found soem huge babys and they ask them for help. Nami understand what their feel right now so she told Sanji save them. And the soliders found the trace on the prision's door, they know this is the same power with Doctor Vegapunk. On the other hand, the birdwoman send two animal soliders attack Luffy but failed finally. And we can also infer something from those animal man, maybe they are all experiment for "M". Think about the devil fruit, maybe "M" want to research the special way of animals.
So Punk Hazard has become the central of three parts: Luffy, "M" and Smoker. Maybe also talking about the warriors in the island. But why "M" catch so many little guys in the Biscuits Room? What's the relationship between he and Doctor Vegapunk? What's the strage building mentioned by Brook? Still too many puzzles exist at Punk Hazard!