It's still a bit peculiar the way the goblin was burned by his magic, since he didnt used fire to do that.
Hypothesis: The 'magical energy' may originate from his soul, and it has the power to increase the energy of natural phenomena.
If you apply magical energy to fire, it turns blue (blue fire is hotter); if used on an electric spark, it ionizes air more easily and you get lightning. If you infuse magical energy into a being already brimming with it, it overloads and burns.
If I'm correct, this means he might be gradually harming himself by recklessly using his energy, weakening his soul. Alternatively, the soul could have an infinite supply of energy, and he might be actually strengthening it. Let's see how this unfolds.