After a fair amount of time spent researching and seeking, Yugi hasn't picked up the ritual specifically, but he is coming to a pretty alarming conclusion: the Sundering Circle was, by virtue of its presence, critical to the ghost dragon returning to a state of undeath. Indeed, it seems to be a startling blend of the Sundering Curriculum and... something else entirely.

Whatever the ritual is, almost certainly it won't work right based on this knowledge. But maybe more needs to be done?