When The Bomb went off in Faire not only was magic twisted, but so was the barrier between our worlds. At seemingly random times the air will sparkle and the two worlds will temporarily become one. This is called the Shift.
It seems to happen more often in more corrupted areas and for longer periods of time, but that is the only prediction anyone can make about the Shift. It often leaves devastation in its wake as the creatures and wildlife of the corrupted Fae world roam the streets during this time. When it ends, everything goes back to its separate worlds and only the destruction it caused stays.
Wielders of magic have to be especially careful during this time as magic becomes more powerful, but it’s harder to control.