He was a "Shang" (ཞང, imperial affine) of Tibet emperor, and Trisong Detsen trust him very much.
With his help, Trisong Detsen purged his regent Mashang Drompakye, and exiled Nganlam Takdra Lukhong to Changtang.
Bon supporters were forced to convert to Buddhism, their cannons were buried into ground or throw into water.
The debate was between the Chinese and Indian Buddhist traditions as they were represented in Tibet.
Finally, Kamalaśīla won the debate, and Moheyan was driven out of Tibet.