I finally have a big enough break to respond to this. Thanks, Cavni, for opening up the thread to use cases. Cavni said: In the process of re-optimizing Advanced Fog of War to facilitate performance improvements and interaction with Dynamic Lighting, we continue to have unintended and undocumented use cases be… brought to light. :P Take 1d12 pun damage. :) Advanced Fog of War used to work by checking every cell on the map to see if player controlled tokens had vision there. For many users, this slowed Roll20 to a halt. With Get a New Look , we refactored the system so that it no longer checked every square: now it measures out from the player controlled tokens and then checks for any obstructions like Dynamic Lighting. This efficiency opened Advanced Fog of War to a lot more people. I think I had a very different experience compared to some people. AFoW never really had bad performance for me before the rewrite. Sometimes it may have been slightly slower, but in general it worked well. In contrast, for basic use cases (i.e. 5e darkvision), the new system works well, but there are times when it grinds to halt in ways that I never experienced before the rewrite. The most significant slowdown I have experienced is when AFoW and Global Illumination are on at the same time, a combination that was not problematic before the rewrite. Indeed, the bug reports for massive slowdowns on large maps seemed to spike after a March 29 patch: March 29: Fixed an issue where AFoW did not reveal using DL vision radius multiplier Fixed an issue where Tokens with sight did not have infinite-ranged AFoW vision when Global Illumination is on Before that, I never had a problem with AFoW and Global Illumination, and I suspect no one had a problem between Jan 29 and March 28 because AFoW was only checked in a limited radius around the token. However, the fact that the system no longer checks every cell means that when it checks on a token that doesn’t have any direct vision, it goes “oh, I don’t have to measure out anything for this token.” That’s why the token is plunged back into darkness if the light source disappears. Reverting to the previous method of checking every cell would make Advanced Fog of War slow and (for many) unusable again, but we understand that the unintended use case here served other needs. If you used Advanced Fog of War in this way, it would help us if you could explain what you were trying to do (such as share a torch between multiple party members) so we can look at new ways to solve that need! Our dev team will be diving back in to take a look at what we can create here, and we will keep you posted about what we find. An Example of the Original AFoW Behavior So now, why did I never have a problem with AFoW performance? I suspect there were a few reasons: Only player-controlled tokens had vision. I am not sure, but I suspect that NPC tokens with vision were causing the engine to go through additional AFoW calculations before the rewrite. I used an optimization that I now think the Roll20 team did not expect / intend. I used the token's View Distance for every player-controlled token with vision whether it generated it's own light or not. The first may or may not have helped, but I believe the second is why I never really had issues with AFoW. The following example is intrinsic to how I understood AFoW to work before the rewrite. I keep coming back to it because: It is from a product I released around September 2018, and the image is from the product page on the marketplace. I am able to create a clean game that has the settings as they were when the promo image was captured. It has a minimum of moving parts. There are only two tokens and no DL lines. In the following image, it looks like a player token is moving across a map and clearing fog of war. In actuality, that token emits light but is only controlled by the GM. The players control a 1-pixel token hidden in the corner of the map (shown selected). As the party explores the map, the GM moves the light token, changing what the players can see, and clearing fog of war. The tokens had the following ownership settings. The player token is on the left, and the light token is on the right. Then the vision settings. Again, player on the left, light token on the right. Notice that the player token has a reveal distance that covers the entire map. What I came across is that fog of war would not be cleared for the players if the player-controlled token had a blank View Distance. If I set the player token's View Distance to 100 miles and then moved the light token every square on the map at least once before returning it to the center, I got a result that looked like the following mock up (imagine the stair-step reveal of the fog of war border). The fog of war was cleared by the external light source, but only within the player token's View Distance. What I Think Was Happening I play D&D 5e, and the usual Darkvision distance is 60 feet. I set the AFoW View Distance to 60 feet on every player token whether the token emitted light or not. I believe this is why I never really had performance issues with AFoW and why all the tokens, including those that did not emit light, had AFoW clear fog of war. Whether the token's were on a map with torches everywhere, a single token projecting moonlight, a torch token the moved along with them, or Global Illumination, AFoW would clear fog of war for a player on illuminated squares within 60 feet of their token. It was not perfect; light further than 60 feet from the player token did not clear fog of war. However it worked regardless of the lighting on the map, and 60 feet was usually good enough. I suspect the following quote from the AFoW entry in the wiki (taken from September 2018) was coming into play: Any value entered in the View Distance under the Advanced Fog of War section will supersede any value you have in Emits Light. When I first started playing with AFoW, I must have started with a token that did not emit light, because I found that the token's View Distance had to be set to get fog of war to clear. I then assumed that was the requirement for every player token, including those that emitted light and assumed that View Distance was used as a lever to balance performance vs how much fog of war was revealed. I never realized that tokens that emitted light did not need the View Distance set until after the rewrite. I suspect that one of the places where performance was bad before the rewrite was on pages with AFoW and Global Illumination. That seems like a prime place where, as Cavni indicated, AFoW would check every square. On a large map, that might take a while, but my players and I never seemed to have a lot of trouble with that. I suspect that setting the View Distance of the tokens limited the scope of the AFoW checks, even with Global Illumination activated. Suggestion for Restoring the Desired Behavior I see restoring the behavior of the player token's View Distance (now Reveal Distance) as fundamental to restoring the overall behavior of AFoW. Before the rewrite, View Distance restricted the scope of AFoW calculations on a map with Dynamic Lighting activated. I never used AFoW on its own; I did not even realize that was a possibility. My guess is that the behavior of the token's View Distance after the rewrite is the same as if AFoW had been used without DL before the rewrite: fog of war is cleared within the View Distance radius around the token. Having View Distance always clear fog of war within that radius of the token seems like a good choice while DL is off. However while DL is activated it is blocking the desired behavior of fog of war because the setting provided some important functions before. I believe that implementing the following changes would place AFoW in a position to make the maximum number of people happy: Change Reveal Distance to limit the scope of AFoW calculations for a player to within its range rather than just clearing fog of war. This would allow customers to limit the performance hit from AFoW even on maps with Global Illumination. A 60-foot Reveal Distance would cause a number of squares to be checked as shown in the following picture. A 60-foot View Distance comprises a square with 25-square sides and 625 grid squares. 136 of those are outside of the radius (34 per corner). This means 489 grid squares would be checked to see if they were illuminated as opposed to the thousands of squares on larger maps. Do not have Global Illumination override a token's View Distance, at least not when it has been set by the user. I suspect that this will avoid the problem with AFoW and Global Illumination on large maps like Storm King's Thunder 's Eye of the All Father map. A token must have "Has Sight" checked to contribute to clearing fog of war with AFoW. Decide what the default Reveal Distance should be when a token has sight and the Reveal Distance. Possible values are 0 or a user-entered value on the game or page settings. Tokens that emit light could also default to the range of their light (bright or dim light based on the page settings). Add a note to the wiki that Reveal Distance clears fog of war when DL is off and limits the range of checks when DL is on. Implementing these changes should get scenarios such as the following working again: My overland map described above. A party carrying a torch token through a dark dungeon. As long as the player tokens stay within a reasonable distance of the torch token, fog of war is cleared. AFoW and Global Illumination as described above. A 5e human walking from a lit room to a dark corridor to another lit room. Only the two rooms and a bit of the corridor would show up as cleared in fog of war. A player token emitting directional light such as from a flashlight or hooded lantern. Only the illuminated squares in front of the token should be cleared in fog of war.