Pokémon - Pokémon XYSider's post back in 2014

While everything on that post should be taken with a grain of salt, it has much more clothing when you consider how some of the elements of said "leak" have materialized throught the years.
Most egregious would have to be everything in Gen 7, from the Ultra Beasts to the Ultra Recon Squad from USUM. Which while not creatures from another planet, alternate dimensions check out as well. (if they come as hamfisted or not is up to debate)

Not that I'm a fan at all of the aliens storyline, personally I think it would have been the hugest shark jump in the entire franchise history (and not shown here, but no one in the thread actually cared for anything XYSider had to say, either because of how outlandish it was or just because everyone's eyes where on gen 3 remakes). And while I still pick the final XY's plot every other day, it's evident that most of it was barely a first draft.
The Prof. Sycamore/Lysandre twist much have been extremely clever for GF's standard, but might actually explain why the fuck on XY Lysandre's reveal as the boss of Team Flare comes as a surprise to everyone, when it clearly shouldn't.
And the mascot legendaries 0 lore or impact beyond acting as McGuffins for the Team Flare scheme.

It's just a facisnating "what if" scenario, especially when you consider this was posted 5 years ago.