George R. R. Martins A Song of Ice and Fire series inspired the main legendaries typing
Someone actually began spreading the rumor that the two main legendary Pokmon of X and Y, Xerneas and Yveltal, were going to be Ice/Steel and Fire/Dark respectively. It was theorized that this was a nod to George R. R. Martins popular fantasy series, A Song of Ice and Fire. Some rumors even theorized that they could exchange their element types at will.
The Bond System is going to replace Happiness
Mr. XY was pretty close to getting this one right due to the addition of Pokmon Amie. He claimed that Pokmon in X and Y would feature Bond levels with their trainers that would grant perks like bonus battle experience, which basically turned out to be true. However, he also claimed that high Bond levels would result in stat boosts, which, sadly, is totally false.
Eevee evolves into Sylveon by way of Bonding (and it's Normal-type)
Much to the dismay of Eevee fans everywhere, Mr. XY claimed that Sylveon was going to be a Normal type Pokmon that evolved based on its Bond level with its trainer. While it is true that Eevee evolves into Sylveon due to its affection for its trainer, the Normal Eeveelution part was false. Thank Arceus for Fairy types!
There will be a daycare for EV training
Hardcore Pokmon fans are no strangers to the tedious grind that is EV (effort value) training, a form of discipline that hones a Pokmons greatest skills. Horde battles (and Super Training) have made EV training trivial, but a theory was being circulated for a while that X and Y would include a Tame Park where trainers could deposit Pokmon to be automatically EV trained. I guess that idea was too good to be true.
Wireless co-op is going to be possible
The theory behind this is actually pretty cool. The host and a friend would be able to take on wild Pokmon and other trainers in cooperative double battles and even earn experience for their own Pokmon independently as they moved through the narrative as a team. I personally would have loved to go through the story with a friend at my side but, alas, it wasn't the case.
Those without 3DS friends can use NPC partners
Never fear, those who dont know any other 3DS owners! It was said that Pokmon X and Y would include NPC partners you could hire at a juice bar located in every town if the game got too challenging for you. The funniest part about this rumor? The idea that Pokmon X and Y would end up being too challenging. Ha.
There are going to be banks
In what was thought to be an attempt to teach children responsibility and money management, Mr. XY claimed that excess cash could be stored in banks located in the game that would result in interest and special gifts after depositing certain amounts. Pokmon Centers would have ATMs for easy access to your funds. This didn't end up being true, but totally sounds like it could have been.
The rival faction is Team Gear
Mr. XYs guess was as good as anyone elses when it came to the evil syndicate of the new Pokmon game. He said the neer-do-wells of X and Y were going to be the purple-clad Team Gear. Their fancy sigil was supposed to be clock hands. Though I suppose a cog would have made more sense...
Team Gear can time travel...
In a wild rumor, it was said that Team Gear had the ability to travel back in time by using special watches and mirrors, affecting the past to change the future. As the protagonist, it would have been your job to stop them from disrupting the timeline.
...and so can you
Of course, stopping time-traveling lunatics would require some time-traveling of your own. Mr. XY said you would be able to explore the same region in two different times periods, 30 years apart. In one instance you would have had to travel backwards in time and catch a Munchlax on the road so it isnt blocking the path as a Snorlax in the future. Cute! Also, fake.