*BOOOOOOOOOOOOMMM!!!*
The explosion that followed was muffled, contained within the dragon's sealed jaws, but it was no less devastating in the slightest. The creature's own red flames, compressed and concentrated within its closed mouth, became a weapon turned against itself in the most brutal way possible.
The dragon's head began to expand like a grotesque balloon, the scales stretching abnormally, beyond any reasonable limit.
Then, the explosion erupted from within, sending fragments of bone, scale, and flesh in all directions. Black blood rained down across the crater like a gentle shower.
It would be safe to say this was done mostly by the force of the explosion rather than the flame, because the red flame would have been too merciful to spray out blood. It would have erased its head into nothing.
