The puca is a shape-shifter and is often seen in the form of a black animal or a black half-animal. When he is so inclined, he favors humans by enabling them to understand animal speech and by protecting them from evil spirits. He also bedevils graverobbers
In English folklore the puca is known as puck, a household spirit who in medievil times was viewed as having a particularly malicious nature and was often identified with the Devil.