the only way to get it is to trade it from Pokemon diamond or pearl you can get it on diamond and pearl by special events
There is no temple of the sea in Pokemon Platinum. In order to get Manaphy in Pokemon Platinum you need to go to Manaphy's special event at any Gamestop (special events are very rare). The temple of the sea isn't in the Sinnoh region.
There are a lot of events on Pokemon Platinum.
No; you cannot catch the three Regis in Platinum, UNLESS you have obtained a special Regigigas through some special events.
You need to download it.
I think you have to find a special pokemon
yes, there is one, but in order to get it, you must get the azure flute either through an action replay code, or get it at special events
it already did i think
Indeed you can. Arceus however is only available in Pokemon Diamond, Pearl and Platinum's special distributions events. You can check pokemon.com for the latest information on this pokemon :]
You dont. DARKRAI (no C, dude) was found in Diamond, Pearl, and Platinum if you had the special Members Key item, which was given away at special events. Check the Pokemon website to see when they will be giving them out next.
Unfortunately the North American event has passed for receiving Shaymin. It's the only legit way to retrieve a Shaymin in Platinum. Nintendo has to release it through one of their special events.
check serebii.net for info on upcoming events for Pokemon Diamond,Pearl,Platinum.