"One Piece" Chapter 812 spoilers deal with "Black Leg" Sanji and Master Nekomamushi. The former is a pirate and the Straw Hat Pirates' cook while the latter is a feline mink and the Whale Forest's guardian on Zou.
In "One Piece" Chapter 811, which is available on Manga Panda, it was revealed that Master Nekomamushi and Duke Inuarashi were more important than their status as kings of the country. As one of the Mink fighters named Pedro said, "The world is waiting for their word."
There is a possibility that Pedro was referring to Master Nekomamushi and Duke Inuarashi as the actually leaders of the Revolutionary Army considering that Dragon recently called for the reunion of the leaders.
Monkey D. Luffy and the gang were on their way to meet Master Nekomamushi in One Piece" Chapter 811, as well. More details about Master Nekomamushi and his perception on the battle with Jack the Drought will be revealed in "One Piece" Chapter 812.
It is likely that Master Nekomamushi will reveal in "One Piece" Chapter 812 that he and Duke Inuarashi are members of the Revolutionary Army.
Another "One Piece" Chapter 812 prediction is that the Big Mom Pirates have captured "Black Leg" Sanji and Donquixote Pirates Scientist Caesar Clown. Fans of the Japanese manga series written and illustrated by Eiichiro Oda were excited about the possibility of the Straw Hat Pirates are fighting the Big Mom Pirates in the future.
According to one of the "One Piece" 812 predictions on Manga Helpers, the appearance of Big Mom Pirates confirmed that "Black Leg" Sanji left with them along with Donquixote Pirates Scientist Caesar Clown.
Also, "Black Leg" Sanji may have offered a deal to Pekoms to allow the Big Mom Pirates to leave the Phantom Island. This will also save the Mink Tribe from further devastation.
On the other hand, "Black Leg" Sanji and Donquixote Pirates Scientist Caesar Clown were nowhere to be found and the former was still able to send a note to Monkey D. Luffy. Thus, it is also possible that the two have not been captured in "One Piece" Chapter 812.
Another possibility is that "Black Leg" Sanji and Donquixote Pirates Scientist Caesar Clown have managed to escape from the crew of the Big Mom Pirates.