The princes of the seas: powerful pirates that aren't part of the Emperor crews, but are still powerful and pretty influential on their own.
The black market: an alliance of merchants who sell illegal staff, they hire powerful Warriors, Pirates, Criminals etc. To protect their products during transportation. They are as powerful as the WG, but they do not have a leaders nor any political ambition, their only goal is to profit no matter what. They are considered as a neural power.
Mafia: a criminal organization with powerful members that together can rival both the Emperors and Marines. As a criminal organization they work with all sides without chosing one or the other.