金盔晃日，金甲凝光 A Golden Helm, a Golden Mail
那大聖停立門外，見那妖走將出來，著實驍勇。看他怎生打扮，但見那：那大圣停立门外，见那妖走将出来，着实骁勇。看他怎生打扮，但见那：
逐句解 Line by line
The Great Sage stood waiting outside the gate; and when he saw the fiend come striding forth, he was in truth a valiant sight.
著實 is an adverb, "in very truth," with 著 read zhuó — not the little ongoing-action marker it looks like. 走將出來 uses 將 as jiāng, the slot the vernacular storyteller drops between a verb and its direction of travel.
See how he was arrayed. Behold:
但見那： is the announcement that a set-piece description is coming — the equivalent of a camera pulling back. By house rule the announcement stays in the prose segment; the poem starts on the next line.
A golden helm that dazzled the sun, / golden mail that gathered the light.
The two verbs are set against each other on purpose: 晃 throws the light off, 凝 holds it in. Four characters to a clause is where an armour-poem always starts, and it will widen to seven as it goes.
From the helm streamed a plume of mountain-pheasant tail; / over the mail a gauze robe of pale goose-yellow.
山雉尾 — pheasant tail-feathers, the plume of a Ming officer's helmet. 羅袍罩甲 is a gauze surcoat worn over the plate, so the fiend manages to be armoured and well-dressed at once.
The armour-cord, coiled dragon-wise, glittered with colour; / the heart-guarding mirror blazed about his eye.
勒 reads lè — the standing fix; the automatic tool offers the colloquial lēi. 勒甲絛 is the cord that laces the cuirass shut. The 護心鏡 is a real piece of Ming kit: the round polished plate over the heart, here made to blaze.
Boots of deerskin, dyed with pagoda-tree bloom;
The ； at the end of this unit ties it to the next as a matched pair. Following the ruling made at chapter 17, such pairs are kept split, each half standing as its own verse unit.
an apron of brocade, worked in willow-leaf pile.
柳葉絨, "willow-leaf pile," describes the shape of the nap or the stitching on the apron. Notice that 鹿皮靴 and 錦圍裙 bring the description down to the feet: an armour-poem works head to toe, and this one keeps the order exactly.
In his hand a keen three-pronged steel trident — / no lesser figure than the Illustrious Sage of old.
And now the compliment that is really a warning. 顯聖郎 is Erlang — 顯聖二郎真君 — the one adversary who ever beat Sun Wukong in a straight fight, back in chapter 6. Erlang's weapon is a three-pronged trident, and the fiend is holding one. The Pilgrim is going to need the warning.
The armour-poem is a fixed station of the vernacular novel, and this one is orthodox down to the character: helm, plume, robe, cord, mirror, boots, apron, weapon, working steadily downward and closing on a comparison. What is not orthodox is the comparison chosen. 不亞當年顯聖郎 sets the Great King of Yellow Wind beside Erlang — the only opponent who ever beat Sun Wukong outright — and puts Erlang's own three-pronged weapon in his hand.
The prose tells us the Pilgrim finds him 著實驍勇, genuinely valiant. It is worth noticing how rarely he grants anyone that. Across six units of verse the narrative is arranging for the reader to take this demon seriously, so that the defeat closing the chapter's first movement arrives as something other than a surprise.