There's an old legend among demons about a cursed artifact. It was called the Helmet of Shadows, and those who wore it became forever prisoners of their own minds.
One of the artifact's victims was a demon mercenary named Tignas. He found the helmet in the depths of a buried cave. At first, the artifact was simply a trophy, but when humans waged war against the demonic garrisons, Tignas decided to use the find in battle.
When the helmet touched his head, the demon heard a whisper. Quiet, barely audible. He paid it no mind, for what is a voice in his head compared to the fury of battle?
Tignas fought valiantly. But with each death, the voice in his mind grew louder, more insistent. By the time the last man fell, the whisper turned into a haunting roar, and the demon could no longer resist it. He turned and attacked his own.
The allies screamed and tried to stop him, but the Helm of Shadows continued to control the demon. By morning, no one remained on the field. Only Tignas, standing amidst mountains of corpses.
When the madness momentarily receded, the demon realized what he had done. In horror, he grabbed at his helmet to remove it, but the metal seemed fused with his flesh. He tore at it with his claws until streams of black blood ran down his face, but it was all in vain.
The voice commanded him to return to the garrison and slaughter everyone who remained there. Tignas knew he couldn't resist for long, so he fled into the dense forest, found a cave, and sealed the entrance, condemning himself to eternal imprisonment. The last thing he heard before the darkness engulfed him was the Helm's quiet laughter.
Centuries have passed since then. Legend has it that somewhere deep in the forest, a collapsed cave can be found, and within it lies a skeleton with a cursed helmet. And it's best if no one finds this place.