Flash Blade

A typical looking +1 magical greatsword, made for Graath.
After making a successful attack with the great sword, the user may activate it to cause a split second flash of light to erupt from the blade.
All creatures within 30 feet with darkvision must succeed a WIS save (DC 15) or be blinded for 1d4 rounds.
This feature may only be activated once per turn, multiple uses of the feature do not extend the duration of the blindness.
The blade may be activated a number of times per day equal to the user’s proficiency bonus.

We got this item as a reward from Bron in session 10 - Zayne's dead, baby.