So I found a way to get any pokemon on ORAS. This doesn't work for the new 3DS XL tho.

1. First of all, you want to clear your history and your cookies on your browser.
2. Access the box and on the first box, leave the first spot empty. If you don't clear this spot, the pokemon currently on it will disappear.
3. Close your box, and don't move; just click the home button.
4. Access your camera by either using L or R, and click on the QR code button (bottom left)
5. Use this sheet: https://docs.google.com/spreadsheets/d/1IgF-vKODrGw98JxilGwGRQ2gncAE4gVEhLoVAtxWrzY/htmlview?usp=sharing&sle=true, choose a code and use it. If it doesn't work, it's due to the dark background; open the image in another page and it should work.
6. A error thing should pop up. That means it worked. Go back to your game and check your box!

PS. The pokemon won't show in your pokedex. To do so, you can put it in the pokemon bank and take it back. Trading should work too.
Source (with images!): http://imgur.com/gallery/OJMaJ

Enjoy!

This is very useful, but it's still blatant cheating and not for everyone. As for me, I stopped caring about dex completion after soulsilver.

Yea, there are too many Pokemon now xD. But if you missed an event because you don't live in Japan, you can activate it using this... well, glitch? (Yep, there is a section for events too)

I'm quite impressed how some people can break the things. I don't know if damage can be done to the console tho, we should be careful. Kids will probably find a way to mess it up.