All creatures and objects within the area of effect are hidden with a hidden DC of 10 + UNP (your UNP, not theirs). This is a minor illusion. If a creature successfully Disbelieves it, then they can see everything that was hidden in this area. Creatures that become hidden by this effect can move freely within the area and remain hidden as long as they do not leave the area. If they leave the area, they are no longer hidden and they do not become hidden if they re-enter it. At the start of each of each round, the GM rolls 1d100. On a 75 or higher, some unexpected additional random illusion occurs in the area as determined by the GM.