This comes from the central part of Kerala. Locally it is known as Vishnumaya or Kutti Chattan. It is a folk deity and the worship is mainly confined to South India. His most celebrated temples include Avanangattil Kalari Devasthanam and Kanadi Kuttichathan Kavu. Kutti Chattan is a folk deity in Tamil Nadu as well. But I have not come across any metal images of the Kutti Chattan from Tamil Nadu.
The deity is wearing a crown and is riding a water buffalo. In his right hand, he is carrying a short stick, Kuruvadi, and a bowl in his left hand.
The lower garment is like a skirt, similar to what is worn in Teyyam, but shorter. Upper body is bare. He is wearing the usual set of ornaments arm bands, wrist bands, anklets, chain around his neck and studs in ears. Kutti Chattan is wearing cross thread running from right shoulder to left him. The sacred thread is worn by Brahmans always runs from the left should to right hip.
The water buffalo is also wearing a chain around its neck with a bell attached to it. Curved horns are typical for the water buffalo.
This is four-piece construction Prabhavali, deity, water buffalo and the base. The Prabhavali, topped by Kiritamuka (face of glory) is riveted to the base. The back is not worked on and the image is quite thin.
According to S K Ramachandra Rao in Pratima Kosha, Kutti Chatta is a cultist object of worship and is the central figure in occult rituals involving possession and dance.
It is about 23 cm in height and maybe from the 19th century.