This hollow mask would have been placed on a stone Linga as a way of decoration. 
The Linga on the head and the five-hooded Cobra add to the intrigue. 
This is used in worship and the tell-tale ritual wear adds to the charm. It is from Western India. Mostly Karnataka/Maharashtra.
The bronze is intact, and the features are sharp.  
It is about 5.5 inches/14 cm tall.
A delightful example. 
Shipping by USPS priority posting.