The fifth Bancho is going to be revealed tomorrow.
Apparently someone has been manipulating the D Brigade (Commandramon and his evolved forms) in their conflict with the Bancho's.
The wording is a little iffy on the promo though. Either it was the Fifth Bancho doing so, or he (or she) is going to show up as they were all challenged to battle, and someone else is pulling the strings.
Admittedly it might make sense for a "Rival Gang Leader" to be the last of the Bancho's, given the theme they are sticking to.
Their battlefield will be Infinity Mountain on File Island from the Devimon Arc of Adventure and the first Digimon World game.
Keep an eye out for more news!
Edit: and it looks like the new Bancho is either Gotsumon or Volcamon.
And Yggdrasil 7D6 is the "boss" of this event.
Really the D Brigade needs more members to fill in it's roster of "Cyborg Dragon Military" and this just feels like a waste of an opportunity if you ask me.
Edit 2:
Better picture, still no name yet.
And a RustTyranomon card that looks awesome as well.