In one episode, the Mongols captured a convoy with a high-ranking official en route to relieve the besieged city of Dading.
One of the Mongols dressed in the envoy’s clothes, took his official papers, and proceeded to the enemy city in disguise.
As he arrived, by prearrangement, the Mongol army lifted its siege and departed.
Once inside the city, the Mongol pretender fooled the local officials into believing that they had just defeated the Mongols.
The pretender then oversaw the painstaking dismantling of the city’s defenses and the withdrawal of troops.
After several weeks of disarmament, he sent word to the Mongols, who returned like lightning and easily took the city.
from Jack Weatherford's 'Genghis Khan and the Making of the Modern World'
https://www.amazon.com/dp/B000FCK206