There is no possible way without hacking or cheating. I heard they are bringing Mew back in Pokemon Heart Gold and Soul Silver.
The only way you can get Arceus in Heart Gold without cheating is to trade it from a game that already has Arceus.BTW, your question was in the wrong category, so I'll fix it.
beat the elite 4 then talk 2 the professor that gave u ur starter Pokemon at the start. forgot his name
you cant, you must get it from a trade or cheating,hacking,or glitching
battle and evolve all your Pokemon or trade for Pokemon you don't have because cheating sucks
yes you can but its cheating and its not fun with cheats i finish Pokemon diamond and heart gold without cheating and i have like 3 or 4 level 100 pokemons and allot of legendary from both games.
you can trade
It's Darkrai. You can't get him in Heart Gold.
Pokemon Heart gold is different from Pokemon Gold cuz heart gold has better graphics new Pokemon and new events
You can't without a cheating device, or a copy of Gold, Silver, Crystal, or any of their remakes.
now
Without cheating or hacking, battle heaps, and I mean heaps!