The Dragon King, heeding their counsel, laid aside his precious sword, raised neither cloud nor rain, came up onto the bank, gave his body a shake, and changed himself into a scholar robed in white — truly:

搖身一變, 'one shake of the body and a transformation,' is the novel's stock formula for a shape-shift, and it is still the everyday Chinese for anybody who suddenly reinvents himself. What it produces here is a 白衣秀士, a white-robed licentiate: a scholar. 依奏 is to act on a petition, and 興 in 不興雲雨, raising neither cloud nor rain, is xīng, 'to stir up.' (一 is yí before the falling tone of 變.) The 賦 that follows describes the disguise.

His bearing noble and imposing, he seemed to tower over ravines and rise to the very sky.

丰姿英偉 is a fine and heroic bearing, and 聳壑昂霄, 'rising over gorges, lifting to the clouds,' is a set phrase for a commanding presence.

His gait was measured and dignified, and in all things he kept to compass and rule.

端祥, a variant writing of 端詳, is grave and composed. 循規蹈矩 — following the compasses, treading the carpenter's square — means observing every propriety; it is alive and well in modern Chinese, and it means roughly what we mean by coloring inside the lines.

In speech he followed Confucius and Mencius; in manner he embodied the decorum of the Duke of Zhou.

孔孟 are Confucius and Mencius; 周文 evokes the civilizing rites of the Duke of Zhou and King Wen. Together the couplet paints the very picture of a Confucian gentleman, which is precisely the costume the dragon has picked out.

He wore a gown of jade-colored gauze with a bordered hem, and on his head a carefree scholar's flat kerchief.

羅襴服 is a gauze robe with a horizontal border at the hem — the 襴 (lán) — and counts as formal scholar's dress. The 逍遙一字巾, a 'free-and-easy one-bar kerchief,' is a soft head-cloth folded into a straight band. (一 is yí before 字.)