Prosperity ritual

The Prosperity Ritual  is an event that wither takes place in or not in Shadow the Hedgehog  depending on what path the player takes.

It is also referred to by several other titles, including being called the Ritual of Prosperity, Day of Reckoning and the Promised Time

Overview
The Prosperity Ritual appears to be some sort of sacred or religious ceremony practiced by the Black Arms, evidenced by the various words and titles used to refer to the event. Black Doom appears to have been planning this ceremony for the past 2000 years, as he mentions he brought the Glyphic Canyon temples to Earth in order to use them as weapons for this day.

The ceremony itself is nothing more than the Black Arms taking over the Earth in order to use the humans as a food and energy source, though it's not clear what would have become of the Anthropomorphic animals such as Sonic and Shadow.