You can't get Regigigas in Pokemon Soulsilver or Heartgold. However, Regigigas is available in Pokemon Diamond, Pearl, and Platinum by obtaining Regice, Regirock, and Registeel. Once you have done that, you can take all three of them to the Snowpoint Temple in Snowpoint City to battle a lv.1 Regigigas.
By the diglet's cave. You need to wake up the Snorlax
You have to go to diglets cave and get to the end. Make sure one of your Pokemon knows cut.
Rt. 19, Rt. 40, Cherrygrove City, Olivine City, Cianwood City, and Union Cave. They are uncommon.
Tm 26 earthquake is in wayward cave in a secret area.
Well, you have to get a electricity Pokemon and level it up until it learns thunderbolt simple!
NO
mewtwo
cerulean cave
Cerulean Cave
In cerulean cave
Dark Cave
in mt.silver cave
Southeast from the middle of the cave
There are no legendary in dark cave in soulsilver that i know of, but i know alot of legendaries and I could list some of them if you want.
in dark cave
ice cave
through the diglet cave!