The mercenaries didn't expect that the undead ruler that would appear in the east would be something as abominable as an Undead King. This is a rare mutation of the undead and said to look closer to humans than zombies. Despite not having the same size as the Undead Warrior, its physical strength is hundred times stronger than it. It can even create undeads with its qi alone and as long as it was not killed it would continue to create more of its kind.
Moreover, the strength of this Undead King was stronger than Mu Liao. He also chose to protect his beasts at the end and suffered from the last attack of the Undead King that's why he had lost consciousness.
