The Regis are not found in the wild in HG/SS, you must trade them from D/P/Pt/FR/LG/R/S/E.
you don't
You get a ticket to sinnoh and and pokedex entries are expanded
You need to either battle or obtain them
get National pokedex and the regis
You cannot catch any of the Regis (Regirock, Regice, Registeel and Regigigas) in Pokémon HeartGold or SoulSilver.
i believe your answer is the pokedex
Number 75 in the Heart Gold pokedex is Politoed ^_^
national pokedex
you have to trade them over
Fill up the rest of your Pokedex!
you can't
Dunsparce and Mareep