Universe 5: XXI
The origins, facts, and events of this universe are entirely unknown at this time. No one has had any interaction with the being of this universe, excluding the Vargas who arrived there, and none of the Z-Fighters have detected anything from the Universe 5 balcony. At one point during the story, Bojack notices that XXI is not even in his balcony.
Unknown, but due to speculations and rumors of this character being hinted as the monster that sealed Old Kai inside the Z-Sword then we could guess a divergence 75 million years before age at least. One hint may also be obtained by the fact that the special chapter about Tapion says that Hildegan's birth "took place in all the universes except four of them". Since it did not happen for sure in Universe 2 because it follows different stories, nor in Universes 1 and 10 because the Kais stopped Hildegan's birth, and as long as the divergencies of the other universes took place in a quite recent past, the fourth universe could be assumed to be Universe 5. So far, basing on the information we have, it is possible to make a few guesses: either XXI created a big divergence after sealing Kai, or maybe he, who has shown the ability to create dimensions, has also the power to travel between dimensions. In that case, he might have originated in any Universe, and then traveled to a Universe that is identical to Universe 0, that is a Universe where life did not exist: that may be the reason why he was the only candidate for his universe, and in this case Universe 5 would be a variation of Universe 0.
Possibly one or more, as there was another person in XXI's apartment when Buu tried to infiltrate it.