情性相和伏亂魔 Nature and Disposition in Accord
好行者，一隻手提著鐵棒，一隻手拖著死虎，徑至他洞口。正是：好行者，一只手提着铁棒，一只手拖着死虎，径至他洞口。正是：
畢竟不知此去可降得妖怪，救得唐僧，且聽下回分解。毕竟不知此去可降得妖怪，救得唐僧，且听下回分解。
逐句解 Line by line
Excellent Pilgrim! With one hand he carried the iron rod, and with the other he dragged the dead tiger, and made straight for the cave door. It was thus:
The verse cue 正是： closes the prose segment, per the standing convention. 提著 and 拖著 both take the continuing zhe. He is carrying the corpse to the door as a calling-card.
The Master of the Law, in his calamity, falls in with fiends; nature and disposition, being in accord, subdue the unruly demon.
The chapter's one genuine tag-couplet: announced by 正是：, and therefore standing as a lone verse segment, which is what puts this passage onto the four-chip form. The chapter's four other parallel couplets — on the road up the ridge, at the moment of the abduction, at the post where the monk is bound, and over the Vanguard's body — all stand untagged inside prose and remain prose. 有難 takes 難 as nàn, calamity. 情性相和: 相 is xiāng, the "with each other" reading, and 情 and 性 are the alchemists' pair — feeling and nature, which in this book are the pig and the monkey.
But whether, going thus, he could subdue the fiend and rescue the Tang Monk, we do not yet know; and you must hear the next chapter told before it is explained.
The storyteller's closing formula. 降得 and 救得 are parallel "manage it" constructions and both take 得 as dé; 降 is xiáng, "to subdue." The same pairing turned up in the Pilgrim's boast at the farmhouse door — 捉得怪，降得魔 — and the chapter ends by putting his boast into the interrogative.
Fifty-nine characters to close on. The Pilgrim goes back down to the cave door with the rod in one hand and a dead tiger in the other, and the storyteller sets the tag-couplet over him: 法師有難逢妖怪，情性相和伏亂魔. The Master of the Law meets fiends in his calamity; nature and disposition, being in accord, subdue the unruly demon.
情 and 性 are technical terms of inner alchemy, and the novel has been using them as names all along: 性, nature, is the mind-monkey, and 情, feeling or disposition, is the pig. The couplet says that when the two are 相和, in accord, the demon falls — which is precisely what has just happened, and precisely what the chapter's whole first half made look improbable. They quarrelled about supper, about faces, about who was useless. Then one of them drove a tiger uphill and the other put a rake through its skull. The last sentence of the chapter, though, is a question: 可降得妖怪，救得唐僧？ — echoing, word for word, the boast Sun Wukong made to an old man in a farmyard some four and a half thousand characters ago. The Tang Monk is still tied to the post.