絕他歸路 Cut Off His Way Back
行者道：「你兩個打進此門，把群妖盡情剿除，拆了他的窩巢，絕了他的歸路。等老孫與他賭變化去。」那八戒與土地，依言攻破洞門不題。行者道：「你两个打进此门，把群妖尽情剿除，拆了他的窝巢，绝了他的归路。等老孙与他赌变化去。」那八戒与土地，依言攻破洞门不题。
逐句解 Line by line
Pilgrim said: "You two break in at this gate, wipe out the whole pack of demons, pull down his nest and cut off his way back.
The order is unusually cold for the Great Sage, and it is strategy rather than vengeance: 絕了他的歸路, cut off his way back, is the point of it, and the demons and the nest are incidental to closing the retreat. 盡情 takes 盡 at jìn, to the utmost.
"Leave old Monkey to gamble transformations with him."
賭變化 is to stake a contest on changes of shape, and 賭 is the same verb the Great Sage used in his own verse at 賭輸贏.
Eight Rules and the local god did as they were told and broke in at the cave door; of which no more here.
不題, "no more of this", closes the thread, the same storyteller's formula that ended the previous passage at 緊閉了洞門不題. The two threads are now inverted: last time the door was shut with the demons inside, and this time it is broken open with them still in it.
The Great Sage divides the labour, and the division is coldly practical. The other two are to break the gate, destroy the demons, pull down the nest and close the retreat; he will take the transformations himself. Only the last of the four clauses is strategy, and the rest is what has to be done so that the last clause works.
絕了他的歸路 is the whole of it. The Bull King has been driven out of his own cave twice in this chapter and has gone back in once; if the way back is shut, the chase in the air becomes the only fight left. The plan is made in one sentence and carried out in the next passage without further comment.