nope
you can't catch any of the three regis on any DS game except platnium.sorry:(
It is possible to trade Pokemon platinum to diamond and pearl, but you cannot trade to any other game.
You don't. to Get any of the regis on Diamond, Pearl or Platinum, you would have to trade online with someone who does have one or get it from a Pokemon Ruby, Sapphire, Emerald, Fire Red or Leaf Green
You can not capture any of the regis in Pokemon pearl, diamon, or platinum you have to migrate from ruby, sapphire, or emerald. or trade with someone who has them.
Any game where you have the national Pokedex
It is not possible to get to Sinnoh in Pokemon Black 2. (Or any game bar Diamond, Pearl and Platinium)
It is not possible to combine the White and Black Flutes or any of the flutes in Pokémon Pearl.
You do not need a Wailord to catch a Registeel in Pokemon Emerald. You may need a Wailord or any other water-type Pokemon to surf to the place where you catch Registeel, but other than that, you don't need a Wailord.
It's not possible to trade from Diamond, Pearl or Platinum onto any previous game regardless of what system it was for.
Of course!
For Diamond, Pearl, and Platinum, there is no possible way to scan cards into the pokedex. Any sellers of these games that say it is possible are false.
palkia is only in pearl and dialga is only in diamond