Okay, I need to address a rumor that has been going around.

BE ADVISED, THIS CONTAINS INFORMATION ABOUT POSTGAME EVENTS. SO THERE WILL BE MARKED SPOILERS.

When you are hunting the Ultra Beasts, it is revealed that there are two universes. One where there is Mega Evolution, which contains X, Y, ORAS, and Sun and Moon, and another without it, which contains...pretty much every other main series game.

Due to one line saying that in a universe without Mega Evolution, it would be all but impossible to defeat the Ultra Beasts, a lot of people seem to believe that they wiped out the universe where Mega Evolution didn't exist.

However, a friend of mine just beat the game, and he says that there is nothing in the game stating that it actually happened. So the Ultra Beasts wiping out the first five generations of the game did not happen. It is just a dumb fan rumor that spiraled way out of control.