I'm not sure how many people know about this (probably a lot) but what is said on the title is true. If you have a 3DS and Pokemon X or Y, you can purchase the Pokemon Bank (for free as a download) and get yourself a legendary Pokemon that everyone knows, known as Celebi, the time traveling Pokemon.
There was a time were the Pokemon Bank was not working due to some bugs, and was taken down from the Eshop in Japan for some time, I heard it was never released in North America or Europe yet during that point (unless someone can correct me with this part of the information) but now that it's finally fixed, you now have a chance to get yourself Celebi.
Pokemon Bank is a storage (almost like the ones in the games) were you can store Pokemon for the time being but rather then having 15 boxes of storage like the Pokemon games, you have 100 boxes and you can store up to 3,000 Pokemon. If the membership of your Pokemon Bank is expired then whatever Pokemon you stored in the Bank will be lost forever.
I heard you have to pay for the Pokemon Bank every month, however you can get yourself a free 30 day trial until March 14, 2014. Unfortunately this event already ended in Japan, however, if you live in either Europe or North America, you should be able to get the 30 day trial but again, remember to get it before March 14.
If you're not able to get the free trial before then and you still want Celebi, don't worry, the Celebi event will still continue until September 30, 2014.
If you want to get Celebi and you don't know how, don't worry, here's the instructions:
1) Download the Pokemon Bank from your Eshop
2) Once downloaded, activate the Pokemon Bank
3) The main menu of the Pokemon Bank will show up and press "start" to continue.
4) Sign into the Pokemon Bank (you'll have to use your Nintendo ID) and select the Pokemon game (X or Y) to continue.
5) Brigette (the person in charged of the Pokemon Bank) will give you a gift either Poke Miles or Battle points as your first gift, you can choose either one.
6) Use the Pokemon Bank (I stored 1 Pokemon during my first time using the bank and then during the second time I used the Pokemon Bank, I took the Pokemon back from the bank). And then exit out of the Pokemon Bank.
7) Go to your Home menu and activate your Pokemon X or Y
8) On the Pokemon X or Y menu, click on Pokemon Link, you should get either the Pokemon Miles or Battle Points (depending on which one you chose).
9) Once you did that, exit the Pokemon X or Y game and go back into your Pokemon Bank
10) Sign in and Brigette will give you a second gift (aka. Celebi), accept the gift, exit the bank and go back to Pokemon X or Y
11) Go to the main menu and click on the Pokemon Link again, it should confirm that you got Celebi
12) Go to your game, check your storage box in any Pokemon Center and see your brand new Celebi
I hope this helps many people get their Celebi and to those people who want to complete their Pokedex just like I'm currently doing, this would really help. I hope to talk to you all soon and if you have any questions, feel free to give out a shout out, until then I hope to talk to you all soon.