I casually mentioned, during a local gaming session, my use of chaos bubbles as a wandering monster encounter. When fellow gamer "A" questioned what I meant by that, it took a moment for me to realize this was an encounter of my own devising and not a part of the rules. I'd been using them for so long I'd forgotten.
Chaos bubbles had their genesis in the Dungeon Geomorphs marketed by TSR back in the day. When this result was rolled on my (always) customized encounter tables I would simply remove the geomorph I was using and put a new one its place, rearranging room descriptions and making up new stuff as needed "on the fly." I liked it so much I began using the idea when I drew my own maps, marking out areas ahead of time that would change if a chaos bubble percolated up from the chaotic underdark (new expression for an old idea used in the name of brevity).
The whole idea sprang forth from the understanding the underworld was opposed to the Forces of Law. This, in turn, was inspired in part by the rules about doors opening easily for monsters but resisting the player-character's attempts to open them. Or, the fact denizens of the underworld had infravision but not players ... and a monster entering the service of the players (and Law, presumably) would lose that ability.
As I began to use this idea on my hand-drawn maps, I began to expand upon it. There were often 4 or 6 such areas with the potential for changing if a chaos bubble came up. The appropriate die was used to generate which area was so affected. Players trapped within a bubble's area of effect might find egress from the room or area significantly changed and their maps of the immediate (or larger) area rendered inaccurate. In addition, the players themselves might suffer subtle changes: gems changing value, gold coins turning into less valuable copper pieces or vice-versa, rations appearing or disappearing from their packs, even the number of arrows in their quiver changing.