In this guide, I will show you how to get some rare items on Pokemon Diamond/Pearl.
Mewtwo Rules !
(Mew is cute though!)
Rare Bone
This item is not that rare, but there is a secret way of getting it. After you have defeated/caught Giratina, go back to Turnback Cave and enter the chamber where you battled the legendary dragon+ghost type.You will seee an item and, believe it or not, it is a rare bone ! You can repeat this trick to get multiple rare bones.
Odd Keystone
Go to route 208 and talk to the ninja guy hidden in the corner of a large patch of grass. He will give you an odd keystone. Next, go to route 209 and place it in that old, crumbling pile of stones. After that, go to the underground and talk to 32 people. (excluding hikers)Finally, go back to the 'hallowed tower' and you will be able to battle a wild Spiritomb.
Suite Key
To get the suite key, go to the hotel near Sunnyshore City and stand in the middle of the whole complex. (In case you were wondering where the middle is, it is right outside the entrance hall thing) Next, go one pace to the left and one pace up and press the A button. You now have the suite key.Now, give it to the girl who is missing a suite key. Go inside the building that she is staying in and talk to her and she will reward you with a lava cookie.
Lunar Wing
To get the lunar wing, you must first have the national dex. When you have obtained the national dex, fly to Canaclave City and go to the sailor's house. You will find that the boy is having a terrible nightmare, and, to rescue him, you must talk to the sailor and go to Crescent Island. Once you are there, go to the forest and you will encounter Cresselia, who will disappear and leave an item behind. Pick it up and you will find that it is a lunar wing. Finally, go back to Canaclave and give the lunar wing to the boy.