Unforgiving Marshland
The inability to fly became a major hindrance to Monk Hushu and Crown Princess Shang in the Trial.
Unlike the frozen wasteland and the volcanic region, they didn't have solid ground everywhere to walk on. They tried to use their immortal sense to tell what place was 'solid' enough, but the area seemed to be making it hard to do that with its unique properties.
Their immortal sense seemingly became muffled as it entered the mushy soil, and the muddy waters of the marshland.
Monk Hushu found it strange and looked more into it, before realizing that there was some kind of energy permeating the entire place. This was the energy that made it hard for their Immoral sense to work when going through materials.
The two weren't ones to back down just from this and started exploring the trial grounds.
It didn't take them long to encounter the enemies after that, as they seemingly rose out of the ground as well as the water.