No, you just need to beat the elite 4. You can find regirock in the cavern at the bottom of the desert.
no
Yes, you do need the National Dex if you want to get into the Regirock, Regice and Registeel caves in Pokémon Platinum.
You must transfer them from ruby and sapphire they do that so its harder to get them and you buy their other games you cannot catch the 3 in diamond or pearl. you need to trade them from sapphire,emerald,and ruby(sorry)
202 (Treecko - Deoxys)
you need to have emerald ruby or sapphire i think
you either need an action replay or you need to transfer them over from Pokemon ruby/sapphire
you need REGIROCK, REGICE, AND REGISTEEL.
no
If you want to find regirock or anything that is regi you would need to migrate them. If you want to migrate them you need Pokemon rubi, Sapphire, or emerald then complete the national pokedex. once you complete it, the game you will have a choice on who you want to migrate. when done go back to Pokemon diamond then go to pal park and you can get regirock. GOOD LUCK!
You can't catch groudon in sapphire only in ruby. To get him in sapphire you have to trade him from ruby to sapphire.
You need to buy a gameboy action replay. Look on the internet for clues on codes. Ones you do that, set the "Shiny Pokemon" on. (IMPORTANT: KEEP THE ACTION REPLAY IN THE GAMEBOY)! If you already followed the steps to unlock the cave to the regirock, click on the regirock. Then it will be shiny in battle. Its at same level. Good Luck!
Pokemon # 486. Regigigas. Get him in Snowpoint Temple, but you need to have the three Regis (Regirock, Registeel, Regice) in your party, and you have to trade them from the Ruby, Sapphire, or Emerald games.