Hard to prove it because it was so covered in vermilion paste but this carving is Bhairab - one of the more violent aspects of Shiva. You won't be able to see it on this low-res scan but he has a fine belt strung with human heads and is trampling on a corpse. Although the current temple buildings at Changu Naryan are comparatively recent (circa 1710) many of the carvings around the temple are very much older, including I suspect this image. It is mounted into the wall of a small shrine dedicated to Pashupati (Shiva as "Lord of the Beasts" - when of his more benevolent aspects)