不許幫丁 Stand And Take Three Cuts
我只與你一個對一個，不許幫丁。」行者聞言，叫：「豬八戒走過，看他把老孫怎的？」那獃子真個閃在一邊。我只与你一个对一个，不许帮丁。」行者闻言，叫：「猪八戒走过，看他把老孙怎的？」那呆子真个闪在一边。
逐句解 Line by line
"I will take you one against one, and no helpers allowed."
幫丁 is a hired hand or assistant — literally a helping able-bodied man. The demon is setting the terms of a duel, and the terms happen to be the ones that suit an opponent who has just brought a companion.
Hearing this Wukong called out, "Bajie, step aside! Let's see what he makes of old Sun."
He accepts instantly and sends away the companion he spent a whole argument obtaining. Everything he told Xuanzang about one palm not clapping is abandoned the moment a duel is offered.
The Idiot really did slip off to one side.
真個, really and truly — the narrator is amused. Bajie was promised he would not be made a fool of and has now been posted to the sidelines within a minute of arriving.
The whole negotiation of the previous section is undone here in three sentences, and the book does not comment. Wukong argued his way into a companion by citing proverbs about the impossibility of acting alone, and then waved him off at the first opportunity because a solo duel is more fun.
There is a real character point underneath. Bajie was not brought along to fight; Wukong said so himself — he wanted somebody to stiffen his nerve. Having arrived at the door with company, he no longer needs it.