You can't catch Regigiaas in soulsilver, so you have to trade.
You cannot get Regigigas in Fire Red.
Yah but I forget if you need them in your party you can get them in emerald ruby or sapphire.
No, there is no Villa in SoulSilver.
You get Darkrai by trading in SoulSilver.
Trading from heartgold to soulsilver
You can't get Darkrai in soulsilver.
POKEMON SOULSILVER come with a poke walker and the Soulsilver game
You can't get to it in soulsilver.
You cannot get Zorua in Pokemon SoulSilver.
Impossible to get a blueorb in soulsilver
there is no explorer kit in soulsilver.
it does not exist in soulsilver outside of hacks or trades.