What exactly is it that you have to do in order to get to Route 224. I..

Eater you need an AR or you need to go through the victory road!!!!!!!

You have to get the National Dex and you get that by seeing all Sinnoh pokemon

First, you need to obtain the National Dex. This is obtained by Oak (in Rowan's lab in Sandgem Town) AFTER you've seen all 150 Pokemon in the Sinnoh Dex. An easy way to see them is by battling every trainer in the game.

Once you have the National Dex, your next goal is to beat the Elite Four. You might have already beaten the Elite Four in order to obtain the National Dex, but if you did not, then do so. Once you have beaten the Elite Four and have the National Dex, fly to the Pokemon League Headquarters, and go down the waterfall. Enter Victory Road, and follow that path until you see an old man. Just behind him are stairs. Go up those stairs and follow that path until you see another cave. Enter this cave, and go through that door you see.

In this room, you need to use Defog. If you move up a couple steps, you'll run into Marley, a girl whose goal is also to reach Route 224. So she'll team up with you, and your goal is to reach the far northeast corner of this room. You'll manuever through various paths and double battles, but once you reach the end, she'll give you a little foreshadowing about Shaymin... Anyways, go through that door, and exit the cave. You're now on Route 224!

To get in Route 224 you must defeat the Pokemon league & also complete the sinnoh pokedex. Then you can go through there but theres nothing really there so wait until the shaymin event comes then you are able to catch him there. I am glad to help.

~Twilight_Sasuke~