Giant bat wing

The giant bat wing is an item on the Odd Old Man's list during the Rag and Bone Man quest. It is dropped by giant bats. After the quest is completed you can no longer obtain this as a drop. The bone must be put into a pot of vinegar and boiled over the fire outside the Odd Old Man's house to create a polished giant bat wing before giving it to the Odd Old Man.

Dropping monsters
Giant bat wing