it is a the top of the pokemon center
Only by trading a Squirtle to HeartGold.
Get Eevee from bill in glenrod city or from the betting place. The train him in entana forest. He should evolve there.You can't, except by trading an Eevee to D/P/Pt, evolving it to Leafeon in Eterna forest and trading it back to HeartGold.
by trading with someone who has heartgold becuase grolithe is only in heartgold
No, you can not get registeel in HeartGold or SoulSilver. The only way to get it, is by trading
Trading from heartgold to soulsilver
Only by trading or hacking.
you can not without trading.
by trading from dppt
Hacks or global trading center
Technically,yes you can get Arceus in Pokemon Heartgold,but only by trading it to your Pokemon Heartgold game from Pokemon diamond,pearl or platinum.
Snover is not available in Pokémon HeartGold so the only option to getting Snover in HeartGold is via trading.
with action replay or by trading it