Mask ('Merganser')

Masks are an important aspect of traditional dance, ritual and magic in 'Merganser.' However, masks are not universal across North America. The most well-known masks are from the Pacific Northwest and American Southwest, especially from the Puebloan cultures. The Cherokee and North Iroquoians had a culture of mask-wearing as well. It seems that horse masks were a medium common across the Great Plains, from the Lakota, Cheyenne, Kiowa and Blackfoot. On the internet, I have only found one traditional example of an Ojibwe mask, a facemask as part of a shaman's regalia. The False Face Society of the Iroquois is not supposed to be depicted by outsiders, according to the wishes of the Haudenosaunee nation in real life.

metaphorical masks
Among the Lakota, there is a traditional belief that spiritual, invisible masks would absorb the sins of a warrior while he went to battle and could be returned to the spirit realm to absolve the warrior of guilt.

Navajo
Here is some basic information about Navajo masks. This is an article concerning the Pueblo peoples in general.