牛鬼蛇神

Either cow demons or snake spirits can trace their roots back to Buddhist sutras. As a chengyu first attested in 831 in Du Mu's Preface to the Songs and Poems of Li He:

雲煙綿聯，不足為其態也；水之迢迢，不足為其情也；春之盎盎，不足為其和也；秋之明潔，不足為其格也；風檣陣馬，不足為其勇也；瓦棺篆鼎，不足為其古也；時花美女，不足為其色也；荒國陊殿，梗莽丘壟，不足為其恨怨悲愁也；鯨呿鼇擲，牛鬼蛇神，不足為其虛荒誕幻也。 [Literary Chinese, trad.]

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云烟绵联，不足为其态也；水之迢迢，不足为其情也；春之盎盎，不足为其和也；秋之明洁，不足为其格也；风樯阵马，不足为其勇也；瓦棺篆鼎，不足为其古也；时花美女，不足为其色也；荒国陊殿，梗莽丘垄，不足为其恨怨悲愁也；鲸呿鳌掷，牛鬼蛇神，不足为其虚荒诞幻也。 [Literary Chinese, simp.]

From: c. 831, 杜牧, 《〈李賀集〉序》, translated by J. D. Frodsham

Yúnyān miánlián, bùzú wéi qí tài yě; shuǐ zhī tiáotiáo, bùzú wéi qí qíng yě; chūn zhī àng'àng, bùzú wéi qí hé yě; qiū zhī míngjié, bùzú wéi qí gé yě; fēngqiáng zhènmǎ, bùzú wéi qí yǒng yě; wǎguān zhuàndǐng, bùzú wéi qí gǔ yě; shíhuā měinǚ, bùzú wéi qí sè yě; huāng guó duò diàn, gěng mǎng qiū lǒng, bùzú wéi qí hèn yuàn bēi chóu yě; jīng qù áo zhì, niú guǐ shé shén, bùzú wéi qí xū huāng dàn huàn yě.

Clouds and mist gently intermingling cannot describe his manner; illimitable waters cannot describe his feelings; the verdure of spring cannot describe his warmth; the clarity of autumn cannot describe his style; a mast in the wind, a horse in the battle-line cannot describe his courage; earthenware coffins and tripods with seal-characters cannot describe his antiquity; seasonal blossoms and lovely girls cannot describe his ardour; fallen kingdoms and ruined palaces, thorny thickets and gravemounds cannot describe his resentment and sorrow; whales yawning, turtles spurting, ox-ghosts and serpent-spirits cannot describe his wildness and extravagance.

牛鬼蛇神

1. (figurative) all sorts of bad things, especially people
2. (historical, politics) cow demons and snake spirits

• (Hokkien) 紅蛇赤鼠／红蛇赤鼠