Shang joined the rampaging barbarians and quickly took control over a group of 30 of them. With his strength, it wasn't difficult.
Shang methodically sent them through the Plague Rat Zone so that as few of them died as possible. After all, there were still a lot of powerful beasts around. Additionally, some Mages and Summoners were also hidden around the Zone.
With Shang's Darkness Vision, it wasn't difficult to spot the hidden Summoners and Mages. When he found them, he simply sent a large team of barbarians after them, not giving them any chance to resist.
These hidden forces probably tried to use guerilla tactics to slowly weaken the Grandmountain Kingdom's presence in the Plague Rat Zone, which was a good idea. After all, the barbarians were stupid and roamed around aimlessly like beasts. It wouldn't be very difficult to pick them off one by one.
However, with Shang's coordinated assault, he dealt with several of them.