The df is most likely Law's i guess . Since it's the only one who can give u a eternal life and it's a big deal.
Gomu Gomu no mi being special is meh..
Guess BB is also after Nico Robin if WG is after her. He was certain that Luffy will lost against 2 yanko and wants to capture her before WG.
I think that Oda will conclude 2 yanko saga in Wano. It make no sense to left BM after coming this far...