Nightmare's Blade

weapon name: Nightmare's blade
description: A blade with a dark crystal handle wraped in leather so the blade don't slide off when swung , and the blade is covered in runes. the blade itself is has holes that when a button is presson on the handle, they realease a halusinogenic gas which makes the person who got sprayed by the gas see their deepest fears.
weapon special abilities: halusinogenic fear: makes the person who smells the gas see their inner most fear come to life but not physicaly there, acting as a distraction and leaving the affected person temporarily open to attacks but wont work if that person has overcome said fear.
history: the original weilder of this weapon seemed to have been of Stargazer decent due to the fact the runes on it are after all over the stargazer ruins, and upon wielding the sword Eyrot had earned the ability to call out the shadow hand, hence the fact that a rune appeard on Eyrot's back when he picked up the blade. the ruins in which the blade was found in seem to depict the previous owned having used the blade not only to kill, but to escape, due to the gas spraying mechanism placed on the weapon which made the person face their deepest darkest fear.

Please explain the stunning ability of the hallucinations. What is the duration and intensity of the effects. How much of the vapor should be inhaled for the victim to be affected?