These tools could probably be named better. Fog of War and Advanced Fog of war are part of the Legacy Dynamic Lighting system that will eventually be phased out/deprecated. Permanent Darkness / Explorable Darkness are part of the Updated Dynamic Lighting system that is still being developed, and is currently in what could be considered alpha testing (even though it is being marketed as 'at parity' with LDL). UDL still has a LOT of bugs. Fog of War / Permanent Darkness is a way for the GM to add a black layer over the map. Players cannot see anything that is hidden under the area of blackness. The GM must manually remove the darkness for players to see anything there. Advanced Fog of War / Explorable Darkness is very similar. The area will be completely blacked out, but once a token has a line of sight into the area, it will be uncovered for that token . Once the token does not have line of sight into that area, it will be greyed out as a reference, but you won't see any other tokens in that area. So if you have a map that has no walls and you put a token on it, everything will immediately become visible to that token. But if you have a page with several rooms, as the token moves through each area will be dynamically visible to the token. <a href="https://wiki.roll20.net/Advanced_Fog_of_War" rel="nofollow">https://wiki.roll20.net/Advanced_Fog_of_War</a>