In fantasy novels, how do immortals descend to the mortal world to undergo tribulation?

In fantasy novels, it was a common setting for immortals to descend to the mortal world to undergo tribulation. The process of transcending the tribulation varies from person to person, but generally speaking, Shangxian needed to go through a series of tests and challenges before they could officially transcend the Tribulation Realm. These tests and challenges usually included: 1. Test of Dao Heart: The Exalted Immortal needs to keep his Dao Heart free from external temptations and disturbances at all times to test his willpower and faith. 2. Tribulation experience: Exalted Immortals need to experience various dangers and challenges in different Tribulation Realms, such as sea of fire, mountain of knives, forest of swords, etc., to improve their strength and ability. 3. Turn misfortune into good fortune: In the process of transcending the tribulation, the immortal needs to be able to turn misfortune into good fortune, turn danger into safety, and avoid disasters and dangers to test his wisdom and ability. 4. Test of spiritual roots: Some Tribulation Realms will test the spiritual roots of Shangxian, such as testing their spirituality, wisdom, reaction speed, and so on. 5. Comprehending the Great Dao: Shangxian needs to be able to comprehend the Great Dao and understand the laws and principles of nature between heaven and earth in order to improve their cultivation and realm. Only by passing the above tests and challenging Shangxian could one officially pass the Tribulation Realm and become a true Shangxian. However, the tests and challenges of each Tribulation Realm were different, so the difficulty of transcending the tribulation was also different.