So Law's after something that can help him take down a Yonkou
. I'd say it's a powerful weapon (or the blueprints to it) that Vegapunk left behind, and more importantly, CC doesn't know about it.
I'd really love for Law and Luffy to team up, but the question is which Yonkou he's got in mind - if it's Shanks, Luffy will no doubt refuse, but if it's Big Mam, he may accept the offer.
It also looks like Law's DF comes with a "built-in" defibrillator or something, and Luffy chewing through the chains was definitely weird
...