You read the title right, I may not be the first do discover this yet I would like to share what I have discovered. So, some of you may remember up until 5th gen that you could increase the stats of a lvl 100 pokemon by doing general training such as fighting the elite four, then depositing it into the PC then withdrawing it again. Well I tried to see if this method worked on Omega Ruby because it is the 1st gen 6 game I have owned. That method from gen 5 did not work. Although I decided to breed more Froakie and I found out that the daycare is a tool for increasing the stats of a lvl 100. I checked my greninja's speed stat before the elite four, it was 314 (not its max speed with the nature and IV's it has (which is why i decided to create a new Froakie)) after taking it out of the daycare its speed stat was 315. Now that's not a large difference right? Well this method is repeatable. After going further into the method I discovered exactly how it works. Look below to see the steps.
1) Fight elite four, or fight at a Blissey bash base, using the pokemon whose stats you want to increase.
2) Go to 1 of the two day-cares, it doesn't matter which, and deposit the pokemon.
3) Take pokemon back from daycare.
4) Repeat until your pokemons stats are maxed.
Please not this will take a while unless your pokemons stats are nearly max.
1) Fight elite four, or fight at a Blissey bash base, using the pokemon whose stats you want to increase.
2) Go to 1 of the two day-cares, it doesn't matter which, and deposit the pokemon.
3) Take pokemon back from daycare.
4) Repeat until your pokemons stats are maxed.
Please not this will take a while unless your pokemons stats are nearly max.