The Ritual of Sundering is an extremely powerful ritual that the followers of Agoth, in particular his Vere, use to enable the Realm of Agoth to merge with another place.  The ritual opens up a portal directly to the Void, which allows the all life consuming essence of the Void to seep out and encompass the area surrounding the portal.  How much area is covered is dependent upon the strength of the ritual and the creature performing it, as well as any other enhancements in place – normally it would cover a maximum of 100 square miles, although it has managed to swallow an entire plane before. Once the merging has taken place all life over the area covered is stripped bare and any Souls taken feed the nearest Soul Gardens.  

The first ritual was performed by Gill and Otion Wraithchild upon the plane of Kulthea.  They had journeyed to aid Vere Mezakorah, a powerful Necromancer from Kulthea, who had approached Agoth and asked him to become the Realm Lord of Kulthea; Vere had designed a ritual that allowed the Plane of the Sleepless Dead to merge with another plane.  Gill altered this ritual to attune it to Agoth and thus was born the Ritual of Sundering.  As the first ceremony received its conclusion some local elves, called Reyhan, attacked the ritual and broke the protective circle.  However, the ritual had been concluded and the realm of Agoth entered Kulthea and began stripping the sprits from all those present. Otion Wraithchild shadowshifted away but Gill and Vere were both caught in the attack of the darkness at the same time the Reyhan struck Vere was slain and his spirit became the first to serve Agoth as an Avatar. Gill was stripped from his body and instead of being consumed was fully incorporated into Agoth. Once All Hallows had passed Vere, Necromancers and Minions of Agoth had gone and left behind a large barren area devoid of all life.

This is now the modus operandi of Agoth.  It will send forth a Vere to establish a foothold and recruit more followers to the cause.  In particular the Vere will select one of the natural (most powerful) inhabitants of the plane to be consumed.  This selected individual will be chosen to become a Vere, through a serious of rituals and ultimately by being slain in the correct manner, in order to be elevated to the status of Vere.  Once this new Vere is created they will be able to complete the necessary rituals to draw through the realm of Agoth onto their plane at the next appropriate All Hallows.  

It is worth pointing out that Agoth does not always consume or take the Plane, but only takes the souls of any living encountered.  Also, the whole plane is not always consumed, just part of it.  When All Hallows has passed, the plane is still there, just much diminished in life.  Each time Agoth does this his power grows.

The ritual must always be performed by a Vere, one native to the Plane to be consumed, and must always be conducted on All Hallows Eve at dusk. It will take many hours of preparation, during which time the Vere must not be disturbed.  If the ritual is not concluded at dusk, then a further year must pass before it can be attempted again.

The best way to prevent the ritual is to slay the Vere who is due to conduct it, or at the very least distract the Vere, preventing it completing the ritual at dusk.  

Once the ritual has been completed, you will immediately start to feel the life draining energies of the Void, only more concentrated.  A Soul Harvester will immediately appear at this stage and a further Soul Harvester every five minutes afterwards.  

It is theoretically possible to reverse the Ritual of Sundering by closing the portal, but you would first need to slay any Soul Harvesters that had come through as well as the Vere who had completed the ritual.  Once these had all been slain you would need to have with you something that represents an essence of Agoth (very difficult to come by).  This essence should be placed at the centre of the portal and then as many High Priests and Sorcerers as possible should call forth their respective Spheres and Elements and direct its energies into the essence of Agoth; all present should beseech whatever they believe in to remove the Agothian taint and close the portal.  With luck, this may work.  All of this would have to be completed within thirty minutes of the portal being originally opened, otherwise all life in the area would be snuffed out and their spirits travel onto the Void.