The Bubble Multiverse is the multiverse canon to Umbrella Waffle, and any potential sequels thereof.
Each universe is infinite in all Euclidean dimensions but three, wherein a given universe extends outward in a given distance from its center, like a sphere. All the universes float around in an infinite void, hence the name "Bubble Multiverse". Two or more universes may collide, or "crossover", cracking the surfaces of the bubbles and allowing matter to move between them. However, this is uncommon, and the rifts tend to mend themselves shortly after the universes separate if possible.
The bubble system also allows for universe-level subordination. Groups of similar universes can be linked together, like double-, triple-, etc.-bubbles that intersect at a surface. A smaller universe can be considered a sub-universe of the largest one. The Paper Mario and Mario Kart universes are sub-universes of the Mario universe, for example.
Universes are created (blown) and destroyed (popped) based on events in real life. Sub-universes can be blown and popped as well, as they are just an interesting form of universe. The real exception to this rule is the "special" Mainverse, which nothing blew into existence—it's just sort of always there in the multiverse, likely because it represents Umbrella Waffle itself. It is presumed that the Mainverse cannot be popped, either.
As stated above, all universes exist in the infinite, limbo-like Void. The Void, in turn, contains nothing but the universes and their contents.
Were an object to somehow enter the Void proper, no longer being in any universe, then it would be erased from all universes' timelines, forward and back. This process is known as "retconning", and the object in question has, in other words, lost its "canonicity". Canonicity is, to be clear, the state of existing in a given universe's timeline. If the object somehow managed to reenter a universe, however, then it would become canon agaian.
As all universes exist in the Void, they start out non-canon to any other given universe, unless the two crossover at which point they become canon to each other. In addition, universes send all of their contents into the Void if and when they are popped.
All of the Bubble Multiverse's matter is made of atom-like structures, which are in turn made of sub-atom-like-ic things that eventually turn out to be made of two distinct kinds of particles: gravitrons and antigravitrons, which attract and repel other matter, respectively. At a subparticular level, everything in the Bubble Multiverse is really just zeroes and ones forged into specific patterns that cause events. It is just part of a videogame, after all. These "bits", as they are called, can be manipulated, but this is very uncommon and should not ever happen on a major scale.
In the Bubble Multiverse, time basically loops around in a ring-like shape. This technically means that there can be any number of instances of a given single universe at a concurrent point in time. However, if a universe is far enough away from itself so as not to cause any temporal paradoxes, which it can't due to a paradox being impossible, then that universe is very unlikely to be able to interact with itself at all.The Mainverse stays put at the center of the ring, never moving.