The zombie's advantage was its speed. The mutated bones were extremely powerful, but its movements were very disorganized whether it was scratching or biting. Its movements were not coherent either. In the face of three targets, it was not a serious threat to Bai Lin.
As for Cheng Nan and Fatty, they were completely focused on Bai Lin.
Although Cheng Nan was an assassin, his moves were extremely sinister. It was more like he had been a gangster on the streets for many years and had been fighting street fights. He often attacked from an unexpected angle, targeting Bai Lin's weak spots.
As for Fatty, his many years of Muay Thai experience combined with his experience in underground boxing made him even more powerful.
Muay Thai was an extremely aggressive martial arts with the title of the strongest fighting technique. It had extremely high combat value and felt like a living weapon in Fatty's hands.