you should be able to, don't know why your having trouble... Did you teach your Regis a Hidden Move? If so then you can't migrate, you'll have to go to the move deleter.
migrate
migrate them from GBA Pokemon games
migrate it from ruby, sapphire, or emerald
you cant you can only get regi rock regi ice and regi steel in Pokemon platinum when you have the national pokedex
Migrate each regi from Sapphire, Ruby or Emerald.
Sorry but you can't get them on Pokemon Platinum. You have to migrate regi rock regi steel and regi ice from eiter ruby or sapphire, ( idk about emerald) i hope i helped ;)
Nothing unless you migrate to diamond or pearl. Then you can get Rigigigas
No, the only way to get them is to migrate them from the 4th generation games.
you cant you need to get all 3 regis and Pokemon dimond or pearl and get the nat dex then migrate all 3 regis then go to snow point city temple then do the maze talk to regigigas then you catch him(1 regi is in emerald and the other 2 are in Sapphire and ruby).Azo;I got all 3 regi's in Pokemon ruby.
First get the national pokedex. You have to see all the Pokemon in Sinnoh to get it, then show prof rowan. Then prof Oak will come. Surf down the bottom of Sangem town until you reach land. The walk to pal park. After you get in, you can migrate Pokemon. Insert Pokemon Emerald, Ruby or Sapphire, with the Regi's in, and go to the title screen and select migrate. Then you can migrate up to six Pokemon, BUT if the Pokemon know a HM move, they cant be migrated.
Actually you're wrong you can NOT get the regis in Pokemon diamond, to get the regis you need Pokemon ruby/Sapphire/emerald you can get all three regis there(regi ice, regi steel, regi rock) althought if you migrate all of the regis onto Pokemon diamond you can get regi gigas(king regi) you will find him in the snowpoint temple after beating the elite four. Thanks hope i helped ^.^
you cant