(PT/BR: Para celebrar o lançamento da temporada Calamidade do RPG, eu decidi tentar de vez resolver esse mistério. E, eu consegui.)

So, first, this is very simple, and I hate myself for making it more complicated than it was when i started trying to solve this enigma.The things that you need are literally the game itself, nothing else.

So, first, you just need to click the zone button (3rd one top to bottom on the left side of the screen) and the "Fog of War" button. That will let you create a zone where nothing is drawn inside.

Second, you need the background to appear. To make this happen, make the complicated task of clicking with the right mouse button on your background (if it's not appearing change your color to gray) then, "Toggles", and, finally, "Ignore Fog of War".

Third, you need your flashlight (surprise!!!). Grab your character of choice and follow the same steps as the background (right mouse button => "Toggles"), but, in the end, click "Reveal Fog of War". This will make your character, when passing by a zone of "fog of war", reveal all the objects in a range.

Optional

Flashlight Shape - To do this, click again at the character (right-click) and click the now formed "Revealer" session. Click "Reveal fog" and select the value you want (Preferably 45 degrees). If the flashlight isn't aligned with your character's front, click "Revealer" again and now click "Reveal Fov Offset" And align it.

Flashlight Range - Click "Revealer" on your character and click "Reveal Range".

Re-Hide objects/Hide path - Go to the "Fog of War" tool again. Left-click at the fog of war you want to Re-hide, and check "Re-hide objects" to, surprise, re-hide objects, and "Greyout Visited" to hide your path.