OK I need to unlock new places I have Heatran & Giratina but those are..

Regigigas: battled once you transferred the 3 regis from Ru/Sa/Em. In the Snowpoint Temple in Snowpoint City.

Cresselia: can be seen on Fullmoon Island. After that, she'll run off into the wild grasses of Sinnoh. To get to Fullmoon Island, go inside the sailor's house in Canalave City, and talk to the boy, and then the mother. Then, talk to the sailor, and he'll take you there. Obviously, while you're there, grab the Lunar Wing and give it to the boy in Canalave City. She's level 50, if you happen to run into her [use the tracking map!!].

Heatran & Giratina: you already have them, so...

Manaphy: In Pokemon Ranger, transfer the Manapy Egg. Obtain the egg from a Poke Mart and hatch it.

Phione: Breed Manaphy with a Ditto imported from FR/LG/Em, and hatch the egg.
*Note: Phione can be breeded from Manaphy, but cannot evolve in Manaphy whatsoever.

These last 3 Pokemon require you to go to a Nintendo Event, or to cheat.

Darkrai: Once you have mystery gift, you can go to a Nintendo Event and obtain the "Membership Pass". With this, go to the hotel in Canalave City, and sleep in the bed a night [in other words, save in the bed, and turn off the game during the night. Leave if off in order for this to work]. Then, you'll be given a map in the morning that locates Darkrai's location. Show this to the convenient sailor in the same city, and he'll take you there. Not much more to do while you're there, so go to the end and battle Darkrai at level 70, I think...

Shaymin: Once you have mystery gift, you can go to a Nintendo Event and obtain the "Oak's Letter". With this, go to route 224. To do this, start at the Pokemon League and go down the waterfall and into Victory Road. Go down and then left until you pass an old man. Immediately past him, there are stairs. Go up the stairs and to the right, and you'll see a cave at the end. Go in the cave, and hopefully you'll have defog... Use it. You have to help Mina, I think is her name, to the end. There will obviously be a series of double battles, and sadly, there is no shortcut. So you have to go through most of the battles. At the end, she'll leave talking about an endless field of flowers or something like that. Go out of the cave, and go along route 224 until you reach the end. For me, I was very disappointed at first-- until I found out the use of the route. At the end of the route, there's only a polished rock. However, with Oak's Letter... A route should be extended from where the rock was. Go up this route and in the "endless field of flowers" [sound familiar? >.<] will be Shaymin, at level 30.

Arceus: Once you have mystery gift, you can go to a Nintendo Event and obtain the "Heaven's Pipe". With this, go to the peak of Mt. Coronet and use it between the two pillars beyond where Dialga was from before. You'll be taken to a high place, I guess Heaven, and you get to battle Arceus at level 80. Yes, 80. Hopefully, you've kept the "... Plate"'s from places in your adventure, because with these, you can have Arceus hold them and change his type. These can be very useful, as you can change his type, and the type of one of the moves he learns. And you can change his color, for looks =]

Go to Canalave city, then go to the house by the boatthe kid here is sick talk to the sailor then he will take you to full moon island Cresselia will runaway so you have to chase it.