locked door

You need to have a Member's pass, which you can only get by using Action Replay, or waiting for an Darkrai event to come around. I think to get Magby you must put fire red in your other DS slot, and go into the fuego ironworks, which are around that field of flowers.( I forgot the name of the town)

In order to either of the following, you need to beat the Elite Four and obtain the National Dex, which is obtained from Oak in Rowan's lab in Sandgem Town after you've seen all 150 Pokemon in the Sinnoh Dex.

1. The door unlocks when you use the Member's Pass on it, which is obtained through cheating or by attending a Nintendo Event, which are currently held in Japan, and won't be held in the United States for a while. Once you have, use the Member's Pass on the door, and take a nap on the bed. When you wake up, obtain the item near you, and give it to Sailor Eldrich, and he'll take you to Newmoon Island, where you'll find a level 40 Darkrai.

2. If you have Pokemon Leaf Green game, insert the game into the GBA slot on the DS, and play your Diamond game. Go onto Route 227 and run around on the grass in the area where ashes are falling. You should find some Magby there. A small percentage of them that you catch will hold the Magmarizer, however, and you need that item in order to evolve Magmar into Magmortar.

You can only get the Member's Pass by using an Action Replay or going to a Nintendo Event which is now only held in Japan, and is supposed to stay there for a while. Once you open the door, you can obtain a Darkrai. He will be at level 40. I don't know the specifics about it, because I cheated for one. Talk to everyone there and somehow you will find out where to get Darkrai. For specific info. Go to serebii.net and it will tell you.