no you do not just the Pokemon relicanth and wailord.
For Pokemon ruby you can catch the three regis, rayquaza, groudon, and latios/latias. In sapphire you can catch the three regis, rayquaza, kyogre, and latios/latias. However, in emerald you can catch kyogre, groudon, rayquaza, the three regis, and latios/latias.
All 3 must be traded from either ruby, sapphire or emerald.
You need relicanth and wailord to catch the regis in sapphire/ruby/emerald. You cannot catch the three regis in platinum unless you have the event Regigigas (this event has now ended). If you have the special regigigas in your party, three new caves will open up in Sinnoh and you will be able to catch the three regis.
trade from emerald
Migrate from Pokemon ruby emerald Sapphire
No, they will need to be traded.
You can fight in the battle tower, catch the three regis, search for latios/latias, or in emerald you can catch groudon and kyogre
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 can't get the three regis but, if you have pokemon sapir\rubi\emerald version on the gameboy advance, you can tke the three regis through the pal park in route 221 (in south). *there are three caves that may be the caves of the three regis but i don't know what to do there.
No you cannot get the regis nor any hoenn Pokemon all must be traded to you from ruby, sapphire and emerald.
Trade someone with Ruby,Sapphire,and Emerald.
nothing, there just there to catch to fill out your browser.