>>55060424The first level of the multiverse is based on the fact the the universe is probably infinite. Despite being infinite, we can only see a small portion of it. Everything beyond that is a mystery.
This universe had a beginning, with the Big Bang billions of years ago. Since the entire universe had the same beginning, the same laws of physics apply to this entire universe.
However, being infinite means that anything that could happen in this universe, with these laws of physics, actually WILL happen somewhere. Not only that, it will happen AN INFINITE number of times.
So in this universe, far far away in space, there are several regions that look nothing like our unjverse. However, if you go far enough, some regions will start appearing slighlty like ours. Eventually, you'll find a region of the universe that looks EXACTLY like ours. As well as versions that are similar but with minor differences. And this will happen an infinite number of times the farther you go.
Keep in mind that this is all in our regular 3D space. Nothing about it involves time or other dimensions. These universes are just really far away from each other.
In pokémon, this level of the multiverse is represented by the worlds of the Ultra Beasts.
Using ultra wormholes, you can create "bridges" across space that allows you to reach these faraway universes, with creatures completely alien to the pokémon world. If you go even further, you can even reach a universe that is like a ruined version of Alola, where Guzzlord lives. As well a universe that looks EXACTLY like your own, except the lake and altar of the Sunne/Moone are switched.
Necrozma and the Nebby family live in the hyperspace "between" these universes, which is what allows wormholes to bridge these different regions of space.