Before the battle began, Xue Wei considered his options. First of all, he could choose to use Mind Infestation and take over the fatty’s mind, finishing the battle with a clean suicide or at least confusing him enough to easily execute him. However, this method was incredibly boring.
Secondly, he could use his beast transformation, but doing so was the same as him admitting to being a beast.
Lastly, he could fight with his other abilities, which would be the many martial art techniques he had gotten from the heritage ring and along the way. This would be the most interesting way to fight. A way to be equal to his opponent and a way to test himself while truly enjoying the battle in the best way possible.
The truth was that Xue Wei had a clear advantage. If he wanted to, he could kill his opponent instantly with either Mind Infestation or pure power from his transformation, but there was no fun in doing that to him.