Some months ago, everyday life was thrown into chaos....

A barbarians flaming tribal sword that had not stopped burning since their god blessed it upon them in their first generation of their clan, stopped burning.
Magical circlets and manacles keeping imprisoned outsiders chained to their Abyssal home broke sending out the Vors and Grundels of horror into the realms
Enchanted clockwork cogs and gears that allowed wonderful skyships to fly, lost their powers and came crashing town upon cities.

...

After the initial panic and discord of culture and civilizations, a new realization came about. Your worlds were no longer singular. A vast meeting of divine practitioners, worshipers and philosophizers was held. Not just figureheads from what was known as Faerun and Ebberon, but priests known as Gothi from a place called Asgard, Relic Wardens of a realm called Ravnica, Istari wizards who wore white and grey robes from a region similar to Faerun called Ennor in the elvish tongue. And many more stranger and unbelievable...

This meeting came to the conclusion there were no less then 16 known different universes that have all seemingly been compiled into one universe Of the known mulitverses there was:
Toril (Faerun and forgotten realms and planes)
Ebberon
Athas (Dark Sun)
Ravnica (Magic the Gathering themed)
Istari (Lord of the Rings themed)
Asgard

....

There are known portals/rifts/bridges to and from each of the known universes. Castles have already been erected to protect these Space Bridges as they are being called.

However, there are also Space Bridges that have yet to be explored, or to have an emissary arrive from in a format diplomatic means. More so, there are unsteady Space Bridges that appear and disappear at random intervals in random locations.

Once a barmaid was taking out trash to the taverns dumpster. The trash she threw out vanished in the dumpster as a Space Bridge opened up in the bottom of the dumpster and a monster like a yōkai, ogre, or troll came out of the Bridge. This hulking figures with horns growing out of its head mauled the barmaid as the taverns people tried to kill the Oni as they came to call it. The Space Bridge closed behind the monster leaving them the only option of destroying the beast...
...

Within the last few weeks, the true nature of this singularity event has been discovered as the very gods came to highest of worshipers and told of the tale of the Apocalypse Stone (See Notice)
It has been told from the highest of divine entities that this Stone was shattered into an unknown amount of pieces, and sent to an unknown amount of the multiverses. The closer to the Stone one moved, the more stable that universe became. (The further from a  stone, the more bleeding of multiverses occur (An Oni from the Oriental Realms and a Uraki from Lord of the Rings could be pillaging the planes of Ravnica))