>>52633433>doesn't explain how or why the professor thought up a large amount of mons in the first placeThe professor wanted to create a paradise where past/future Pokemon and modern Pokemon lived side by side. That necessitates a large number of them. As for the "how", the machine was set to automatically produce Pokemon and had been doing so for some time before the game started.
>The professor also "thought up" two versions of VolcanaraStorywise Heath and the professor only thought of or brought in their version exclusives. Sada got Slither Wing and Turo got Iron Moth, there isn't really an explanation for both existing in the same game.
>There is no way of knowing that the magazine the professor or even the people of Paldea saw had mega Salamence in itIIRC you find the Occulture magazine containing Roaring Moon in the professor's lab at the lighthouse.
