This package provides a fast, attractive and easy to use fog of war.
Place a translucent plane above your playing area, on which the Fog of War class renders animated clouds that obscure the world below. And then deploy Beacon objects--either programmatically or through prefabs--which produce visible regions in the cloud layer allowing the player to see just what you want.
Critically, this package's custom shader does very little computation during rendering--instead, all important calculations are performed during the Update phase and only when absolutely needed.