返騙一場 A Counter Deception Planned
我聞得唐僧在那大路上等候。他二徒弟豬精、三徒弟沙流精，我當年做妖怪時，也曾會他。且變作豬精的模樣，返騙他一場。料猢猻以得意為喜，必不詳細隄防。」我闻得唐僧在那大路上等候。他二徒弟猪精、三徒弟沙流精，我当年做妖怪时，也曾会他。且变作猪精的模样，返骗他一场。料猢狲以得意为喜，必不详细隄防。」
逐句解 Line by line
"I have heard that the Tang Monk waits upon the high road yonder."
聞得 is a settled compound in which 得 is the full verb "come to", so it takes dé. Chapter 59 has the same compound twice and reads it dé at both.
"His second disciple is the Boar Spirit and his third the Sand Spirit; in the years when I was myself a monster I met with them."
He names them by species, not by name — 豬精 and 沙流精, the Boar Spirit and the Sand Spirit, and not the usual 沙悟淨 or 沙僧. That is how he would have known them in the years he is remembering. 當年 is again 當 meaning "at the time of", dāng.
"I shall change into the shape of the Boar Spirit and cheat him back in his turn."
返騙, to cheat someone back, is the chapter's own word for what follows, and it admits the ledger openly: the Great Sage spent this same day wearing the Bull's face to rob the Bull's wife. 模 in 模樣 is mú, the fixed reading for the "shape, pattern" sense.
"I reckon the ape, being pleased with his success, will surely not be watchful in any detail."
The whole plan rests on a single reading of his enemy's character, and it is a correct one. 得意 takes dé — 得 is the verb, to have got what one wanted. 為 is wéi, "to be", not the wèi meaning "for the sake of". 隄防 dī fáng writes "to be on guard" with the embankment character 隄, a common Ming way of spelling 提防.
The plan turns on one observation about his enemy, and the observation is right. The Great Sage's weakness has never been fear or want of skill; it is that winning pleases him so much he stops looking at things. The Bull has fought him twice in two days and has watched closely enough to know it.
It is also a plan that only somebody on the receiving end could have made. The Bull was robbed this morning by an enemy wearing his own face, and within hours he has understood the method well enough to run it the other way. 返騙他一場 is not improvisation. It is a copy.
Two details date his acquaintance with the pilgrims. He calls them 豬精 and 沙流精, spirits rather than monks, and he places the meeting 當年做妖怪時 — back when he was a monster himself. Both put the acquaintance well before the journey, in the world the Great Sage belonged to before the mountain.