Shadowcloy

Source Advanced Race Guide

This thin black liquid is stored in airtight flasks because it evaporates quickly when exposed to air. Its cloying vapors cling to a target, obscuring vision for a short period of time. You can throw a shadowcloy flask as a splash weapon with a range increment of 10 feet. A direct hit means the target treats the ambient light as one category darker than normal, with a creature already in natural darkness treating it as supernatural darkness. This effect lasts for 1 round. A thrown shadowcloy flask has no effect on adjacent creatures or if it misses.