The Rock and Inn?

Well, the rock is used for, when you get Oak's letter, Professor Oak will be waiting by it, and once you talk to Professor Oak, you must read the stone, and it will have new writing on it. And in the Inn, there is a guy, and he puts you to sleep, then you awake on an island, and you will be able to face Darkrai.

Hope this helps you!!!

Ahh! You have found the Shaymin Stone! To make any use of this stone, you must obtain an Item called Oaks Letter, available only through cheating or a nintendo event. It is vital in the process of getting the legendary pokemon;Shaymin. As for the door in Canalave, it is the same story. You need the Door Key, and once in there you are transported to New Moon Island, which is east of Full Moon Island, where you catch the elusive egendary:Darkrai!

The rock is the key to getting the legendary Pokemon Shaymin. You need Oak's letter but you can obtain it only through a Nintendo Event or an AR cheat. If you want to get through the door you need another Event item called the Door Key. After you go inside there is a man who puts you to sleep and you wake up on the island where the legendary Pokemon Darkrai awaits you.

Those places are pionts in the game where you can use an item you get through a nintendo event which is held rarely but the easiest way now is to use AR to get the items. The "mirror stone" as you called it is where you go once you get Oak's letter and it triggers a conversatin between you and the professor in which he will ask you to write who has spurred you into being the best you can be on the stone (It doesn't matter what you write, you could write crap or Joe Jonas (not that you would wnt to)) and after that a long road appears and oak tells you it is a road to flower paridise. Home to legendary Pokemon shaymin. From there you can leave to stock up on anything then ride your bike to flower paridise and catch shaymin. Shaymin by istelf is not a particularly good Pokemon, but itcomes with bragging rights otherwise it is pretty much useless. As for the Inn and locked door, one event gets you the door key which you use and a random butler greets you and tells you to lie down on the bed and sleep. You are then transported in your dream to New Moon island where you battle Darkrai. You should stock up before you go to the Inn because once you fall asleep there is no going back. Once you either beat or catch Darkrai you will wake up and leave the Inn and some one will talk to you and say something liike "Did you just come out of that building? That Inn has been closed for 50 yeara." O.o then he will just walk away and you have Darkrai. Hope this helps^^

That shiny rock there at the end of that route is where the Shaymin Event takes place. You need an Action Replay to do so. When you've used the code for it, you will recieve the item, Oak's Letter, from a guy in a green suit in a PokeMart. Take that item to where the event takes place, and you will see Prof. Oak. Give the letter to him. Then, a really long path will open up. At the end of that path is a Lv. 30 Shaymin. Don't be too harsh on it. You don't even have to use a Master Ball to catch it. I used an Ultra Ball to catch my first Shaymin. Alright, the inn in Canalave City is where the Darkrai event takes place. The building will only unlock when you use the Darkrai Event Code. You will get an item called the Member's Card. Take that to the building. It will be unlocked. Go inside. You will then be transported to an island, which is called New Moon Island. You will see a cavern. Inside is a Lv. 40 Darkrai. If you don't want to use a Masterball, I reccomend you stock up on Ultra Balls. Once you battle him, you will wake up and then walk outside. There you go, you now have Darkrai.