Although the Ghost Moon’s unpredictable phases and eerie correlation with rises in undead activity had long marked it an indicator of dire happenings, no one in the Middle Realm suspected its true nature.
Debate still assuredly rages, but most scholars now believe the Ghost Moon was a sky-high portal to the Sixth World, a fluctuating window into that strange, infinite land. When the portal collapsed, perhaps due to massive disturbances in the Sixth World – or, somewhat chillingly, perhaps due to unknown events (sins, if you will) perpetrated in the Middle Realm – the Sixth World collapsed. Without it, the Middle Realm’s dimensional anchor ceased to be, and the huge plane’s metaphysical gravity sucked the neighboring mirror planes inward. A large, stable and powerful world requires, at the very least, an opposite number of equal gravity; when the infinite mysteries ceased, so did the Middle Realm’s place in the Universe. The currents and denizens of the Astral Sea are not kind to freefloating worlds.