Lamaism is mainly professed by the Northern Nu, although Christianity has made some inroads into the southern group.
From the en.wikipedia.org
The Qing government wanted to tie the Mongols to the empire and it was Qing policy to fuse lamaism with Chinese religious ideas insofar as Mongolian sentiment would allow.
From the en.wikipedia.org
Nevertheless, there is some evidence that outside of lamaism, there were practices of tantric human sacrifice which survived throughout the medieval period, and possibly into modern times.