This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Gandabherunda (Hindu)
Gandaberunda (Sanskrit:'terrible-necked') is a two-headed bird in Hindu mythology, a form assumed by the Hindu deity Vishnu. It is believed to possess immense magical strength. Vaishnava traditions hold it to be a form of Vishnu to fight and subdue Sharabha (In Shaiva traditions, Sharabha is a form of Shiva assumed to pacify Vishnu's Narasimha avatara).
The bird is generally depicted as clutching elephants in its talons and beaks, demonstrating its immense strength. In a coin found in Madurai, it is shown holding a snake in its beak. All 2-dimensional depictions show a symmetrical image similar to the double-headed eagle while other images show the long tail feathers resembling a peafowl.