出没无常

Explanation: Suddenly appear, suddenly vanished without a certain, people can not fathom. 　　Usage: The main predicate; as the predicate attribute; with compliment, for the mysterious person or thing 　　Source: Sung Shi Peng, "Wang Zhongwen wide sea of public and _set_ the second son Cole Sapporo": "pirate infested impermanence, particularly the risk of coastal counties." 　　Examples: Parallel to one another in the northwest, deep under the balcony Lingxi fall down, but Yao is not visible; Ling Tung Zhi and on screen, and ~. (Ming Xu Hongzu "Xu Travel Yunnan Tour Diary") 　　Riddle: Palace of hell; submarine Thesaurus:  Surreptitious Unpredictable, appear and disappear mysteriously, Marvelous and unpredictable