The Great Sage Sun stepped forward: "Your grandfather Sun is right here. Give me back my master at once and neither side is harmed; but let you say so much as half a No, and I will see you dead without a patch of ground to be buried in!"

Two nice things in one speech. 孫外公 is a pun on his own surname — 孫 is the family name Sun and also the ordinary word for a grandson, so calling yourself somebody's 外公, their grandfather on the mother's side, is a joke about rank that only works because of what he is called. Wukong makes it constantly. Then, in 半個『不』字, half a "No", the character 不 is being named rather than used — it is the word itself on the table, like saying "don't give me so much as a T of 'no'". So it keeps its dictionary reading bù, where in ordinary running speech before 字 the tone would lift to bú. Quoting a word freezes it. 還我師父 has 還 as huán, to give back.

The fiend roared back: "You bold and reckless monkey spirit! What arts have you, that you dare talk so big?"

甚麼 is shén me. 大言 is big talk. Trading insults before a fight is fixed form in this novel, as much a part of the occasion as the weapons, and both of them observe it exactly.

Pilgrim said: "You filthy creature! It seems you have never seen what Old Sun can do."

潑物, filthy thing, is Wukong's word for this fiend and for nobody else in the chapter — he uses it here and once more as the fight opens. He answers the question by pointedly declining to answer it.

The fiend said: "Your master stole my clothes. It is a fact that I have taken him, and I mean to steam and eat him presently."

實是我拿住了 is a plain statement of fact, and it happens to be one. The fiend does not lie anywhere in this chapter, which is exactly what makes him impossible to shout down.

What sort of hero are you, to come to my door and demand him back?"

取討 is to demand back what is owed you. He is asking by what right — and it is a fair question, which nobody in the scene is going to answer.

Pilgrim said: "My master is a loyal and upright monk. How should there be any question of his stealing any goblin goods of yours?"

忠良正直, loyal and upright, is a formula out of official praise, the sort of thing written on a commendation. Wukong defends his master by character rather than by facts, because the facts are against him and he knows it.

The fiend said: "I conjured up an immortal's manor by the mountain road. Your master slipped inside it, and with his heart set on wanting he stole three brocade-quilted padded waistcoats of mine and put them on. There is the stolen property in evidence, and that is why I took him."

點化 is huà; 將 is the jiāng that takes hold of the object; 背心兒 takes the little er ending. 贓證 is stolen property produced in evidence. And listen to 心愛情慾 — the heart loving, the feelings desiring. That is the chapter title in miniature: 情亂性從因愛慾. The fiend lays out the charge in proper legal form, and the stolen goods are in his hands.

If you really have skill, then match your strength against mine: if you can hold me for three bouts I will spare your master's life; and if you cannot stand against me, I will send you the road down to the shades."

比勢 is to test strength against strength. 敵得我 takes 得 as dé, could manage to; 教你一路歸陰 has 教 as jiào, to make someone do something. Three bouts is the wager. Keep the number — the fight will run to thirty and settle nothing.