I figure before I do much more work on this idea, I would like to see what others think of it. I'm planning on using this image or something similar for it, since it did inspire me after all.
The idea is an anomalous gas mask, but one that was made by someone and not produced for military or commercial use. The mask, once secured on a person, can't be taken off until they die. The little hole near the mouth can be opened and closed, so it's possible to keep someone wearing the mask alive indefinitely. Wearing the mask causes the subject to experience a rate of spontaneous mutations signifcantly higher than is normal. In about 40% of cases this leads to terminal cancer, but in the others it manifests as physical deformities of the extremities and internal organs, espeacially the lungs.
The changes caused in the lungs and skin of the subject make it so that an environment lightly saturated with mustard gas is nessasary for their survival. As the mutations progress, so does a second effect of the mask. Slowly, the subject's memory and personality is overwritten with those of another entity. This entity is never the same from subject to subject, and it's tempermant can vary from extremely hostile to cooperative. Sometimes it speaks a mutated dialect of English, sometimes other languages. The only common factor the entities seem to have is that they apparently come from the same universe.
Through various interviews, the Foundation has put together a rough timeline of that universe, which is largwely identical to our own up until World War 1, which the United States failed to enter until the United Kingdom had fallen to invasion by Germany. The resulting altered war lasted well into the 1950s, and escalated in scale over time until the planet was largely depopulated and contaminated with chemical weapons. The few remaining people either died slowly of poisoning, or adapted to the poluted atmosphere.
What do you think of it?