Collapse of time

The collapse of time was a catastrophic event that was prevented at the end of Pokémon Mystery Dungeon: Beyond the Shadows, as well as its canon reboot.

Cause
The collapse of time was to be caused by the collapse of the Temporal Tower. An unknown force was causing the tower to collapse, which, in turn, would cause Dialga to go berserk. While time itself would collapse as a result, Dialga would be unaffected by this, causing him to rule over a dystopian Mystery World.

Result
The collapse of time was prevented thanks to the efforts of John the Charmander and Rei the Shinx, with help from the rest of Wigglytuff's Guild, Grovyle, and others. The collapse of time never happened as a result.