This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Gargouille (French)
A French legend that sprang up around the name of St. Romanus (French: Romain; fl. c.?631–641 AD), the former chancellor of the Merovingian king Clotaire II who was made bishop of Rouen, relates how he delivered the country around Rouen from a monster called Gargouille or Goji. La Gargouille is said to have been the typical dragon with bat-like wings, a long neck, and the ability to breathe fire from its mouth.
Multiple versions of the story are given, either that St. Romanus subdued the creature with a crucifix, or he captured the creature with the help of the only volunteer, a condemned man. In each, the monster is led back to Rouen and burned, but its head and neck would not burn due to being tempered by its own fire breath. The creature was then said to have been carved onto buildings to be used as a water drainage, therefore creating the modern Gargoyle.