SAD

SAD is a substance produced in a lab within Punk Hazard, D Block. It was first alluded to by Vergo in Chapter 672, then became a more important part of the story in Chapter 681.

Properties
Though what exactly SAD is has not yet been revealed, it appears to have the potential to cause chaos within the New World, depending on the one who wields it. Caesar Clown is the only person in the world who knows how to manufacture this substance. As such, SAD is very valuable, as Donquixote Doflamingo suggested destroying the production room and killing Caesar to prevent it from being stolen and the scientist from being kidnapped, only to retract such suggestions as it would be troublesome for him to lose his supply of the substance.

Punk Hazard Arc
Trafalgar Law apparently went through great lengths to gain access to the SAD production room in Punk Hazard: joining the Shichibukai and then allying with the Straw Hat Pirates. He eventually succeeded amidst the chaos in the lab, but Vergo contacted Doflamingo and reported it. Vergo was ordered to stop Law from taking SAD and kill him for treason, which leads the two to fight in the production room.