As an Action, open the bottle.

When opened, thick smoke pours from the bottle, Heavily Obscuring everything in a 6×6 area centered on it.

At the end of each round the bottle remains open, the smoke's area increases by 2×2 spaces each round, to a maximum area of 12×12.

The smoke lasts for 10 minutes, but can be dispersed by a strong gust of wind.