Flying Gators look and behave very much like winged Alligators or Crocodiles. The single pictorial example of a Flying Gator shows they are green in color with a small pointed spade at the end of their tails. They may also have only a rear pair of legs. It appears they can breathe fire as most dragons can.
A group of Flying Gators are referred to as a "goggle."
Flying Gators are not known for their intelligence. The Incomplete Book of Dragons reveals that they can be easily fooled by mimicking the sound of a poisonous dragon (such as the clicking of a Toxic Nightshade) and they will instinctively scatter, though humans clearly do not look like a dragon!
Flying Gators inhabit marshlands such as the Haunted Marshes and often stay submerged in the water so that only their eyes show. They wait quietly for unsuspecting animals - even other species of baby dragons—to wander into the water, and then strike.
Flying Gators are mentioned once in this Book, as Hiccup notices what is aboard the Roman ship.
|“||An enormous number and variety of dragon species were being held prisoner behind the bars of this cage. Deadly Nadders, Flying 'Gators, Big Spotted Gormlesses, Yellow Vampires, Common or Garden Dragons - you name it, they were all there, trapped together in a furious tangle of talons and wings and fangs, ready to be sent back to the restaurants and shoemakers in Rome.||”|
|— How to Speak Dragonese|
This reference book provides some detail and an image of the Flying Gator.