This invincible demon is likely a reference to the Nibelungenlied (or another story inspired by it), where Siegfried became invincible after bathing in dragon's blood, except for a spot on his back that had been covered by a leaf.
This invincible demon is likely a reference to the Nibelungenlied (or another story inspired by it), where Siegfried became invincible after bathing in dragon's blood, except for a spot on his back that had been covered by a leaf.