This spell is a part of the Psy Dagger spell chain and is found in the Psy Dagger rune stone.
The dagger is not real. This is important to understand, not because it means the dagger is harmless, but because it means the damage it causes comes from somewhere more interesting than steel. The target sees it coming. The target believes it will pierce them. And the mind, receiving that information with complete conviction, does what minds do when they believe they have been stabbed. It responds accordingly.
Psy Dagger is the mentimancer's first lesson in the most fundamental principle of their practice - that the mind's interpretation of reality and reality itself are less different than most people assume. A small, precise projectile of space energy forms and flies to the target, embedding itself just long enough for the belief to take hold before fading away. The 3d6 piercing damage that results is entirely real. The dagger that caused it never was. This means that the dagger cannot be evaded, nor can armor protect against it for what can protect against damage caused by the target's own mind? Instead, the target can attempt a Hard Insight check to determine if they believe the dagger is real at all. Succeeding allows the target to ignore the damage. Failing causes the target to believe and the damage to be real. A critical fail - rolling a natural 1 - means that the target believes in the dagger so much it causes double the damage. Dream is showing the mentimancer, from the very beginning, what belief can do.
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