Question: Based on a local legend, this species of dragon can't fly, but instead covers itself in flame to protect itself from hunters. 

With as little magic as possible, would something like that be possible? 

**More details about the creature:**

* It's about twelve meters long, nocturnal carnivore and is said to have thick scales.
* The flames are not a constant effect, the creature only uses it to scare off hunters.

My question is: **How could a creature like this exist?**

Magic is allowed, but I'm trying to avoid using it as much as possible.

Answer: 
It is a legend that they are covered in flame. No real creatures get covered in flame. But what if they just look like they are covered in blinding bright flames? That happens. Maybe the dragons are **bioluminescent?**

[![bioluminescent ostracod](https://i.stack.imgur.com/wZK8s.jpg)](https://i.stack.imgur.com/wZK8s.jpg)

<http://www.bbc.com/earth/story/20160526-the-organisms-that-glow-brighter-than-any-other>
A cardinalfish (Apogon sp.) spits out an ostracod after it triggers a flash of bioluminescence (Credit: naturepl.com/Alamy Stock Photo)

> 
> But Gerrish has found that the threat of attack provokes the most blinding >bursts of light.
>  "The brightest luminescence of the ostracod is produced when they are
>  preyed upon," says Gerrish. "The ostracods release large amounts of
>  both luciferase and luciferin, which mix and light up the outline of
>  the predatory fish."
> 
> 
> This flash-bomb tactic could be some of the brightest bioluminescence
>  in the ocean.
> 
> 
> 

So too your dragon. It is not on fire, but produces a fire colored flashbomb effect when under pressure. Hopefully it makes use of the time bought to counterattack, or slip way.
All these answers are pretty good, but there is another possibility that I don’t think has been mentioned...

If you take a flammable gas like methane, and pump it into water as it freezes, you end up with *flammable* ice. Cooler still (heh, puns), you can actually hold this ice in your hand as it burns, because the water shields you from the heat.

So am I saying your dragon should be covered in methane/ice? No, well maybe, that’d be cool, but that’s beside the point. What if your dragon naturally made a sticky sort of mucous that was secreted out of its skin. The top layer of the mucous could be as simple as fat and/or sugar based compounds from the dragon’s diet, while the bottom layer could be as simple as some kind of water based slime. Now all you need is a spark, maybe from specialized scales, fire breath, a special organ, all of which were mentioned in other answers and boom, your dragon is covered in flames that will burn until the fuel is gone and then self extinguish once they reach the water based slime coating the dragon’s scales.