Harmonic Negation, Song of Unmaking, the Apocalypse Song, the Great Equalizer. It has many names, but the Song is probably the most common. 

Its exact workings remain a mystery, but its power and connection to the Dread Realm is Undeniable

A Strange piece of Magical technology, first thought to only exist in the Candle Keep, but later seen in the Wastes and now in the Second Star. How it works is not fully understood, but it does allow a limited transportation within Ravenloft. Travelers do no actually travel, but are somehow projected to the location with their being preserved. Should they die, or the portal be turned off, they are shunted out of the portal with no memory of events. Should they return, they come back fine. Others on the far side cannot see the return portal, nor can they travel back. However, objects can be moved in this way.