The Yunmen school flourished into the early Song Dynasty, with particular influence on the upper classes, and eventually culminating in the compilation and writing of the Blue Cliff Record.

When Xuefeng Yicun died, Yunmen began travelling and visited quite a number of monasteries, cementing his reputation as a Chan master.

[2] The area of Southern China where Yunmen lived broke free during the rebellion of Huang Chao, a viceroy of the Liu family.

One day, when Yunmen was 85 or 86, he composed a farewell letter to his patron, the new king of the Southern Han, and gave a final lecture to his monks, finishing with the statement: Coming and going is continuous.

Yunmen was succeeded as abbot by Dongshan Shouchu (Chinese: 洞山守初; Pinyin: Dòngshān Shǒuchū; Rōmaji: Tōzan Shusho; d. 900[5]).

Yunmen was renowned for his forceful and direct yet subtle teaching, often expressed through sudden shouts and blows with a staff, and for his wisdom and skill at oratory: [He was] the most eloquent of the Ch'an masters.

According to Gyomay Kubose: "Yunmen's school is deep and difficult to understand since its mode of expression is indirect; while it talks about the south, it is looking at the north."

As to the records of "Corresponding to the Occasion"[k] and "Inside the Master's Room"[l]: Xianglin and Mingjiao had fashioned robes out of paper and wrote down immediately whenever they heard them.

[8]Despite this, Yunmen is one of the greatest sources of "live words", "old cases", and paradoxical statements that would later evolve into the koan tradition, along with Zhaozhou (Japanese: Jōshū Jūshin).

[n] While his short ones were popular, some of his longer ones were iconic and among the most famous koans: Yun-men addressed the assembly and said: "I am not asking you about the days before the fifteenth of the month.

[10] Despite being a popular place for pilgrimages, the legendary Mount Wutai in Shanxi was ordered off-limits by Yunmen and his dharmic descendent, Linji Yixuan.

[12] The Rinzai master Shuho Myocho experienced great enlightenment after contemplating a Yunmen kōan for ten days.

After the moment of enlightenment, his master Nanpo Shomyo told him: "Yesterday I dreamed that the great Ummon (Yunmen) personally came to my room.

[17] American Zen teacher Robert Baker Aitken explained that the term was used as "a soft stick that was used the way our ancestors used a corncob in their outhouses"[18] Jack Kerouac paraphrased the kōan in his book The Dharma Bums as "The Buddha is a dried piece of turd.

"[19] Wumen Huikai appended the kōan with the following verse: Lightning flashing,Sparks shooting;A moment's blinking,Missed forever.

[20]Yunmen's Japanese name, Ummon, was the namesake for a prominent character in Dan Simmons's Hyperion Cantos science fiction series; Simmon's Ummon was a vastly advanced AI from the "TechnoCore", who reveals key plot elements to the main characters through kōans and mondo (dialogue).