sinjoh ruins
A while back there was a Pokemon movie released and a special arceus was given out via special event on platinum. Trade this arceus to heart gold and put in the front of your party. Go to the ruins of alph research center and they will be surprised that you have an arceus. On of the people will transport you to a place called the sinjoh ruins. Here you will find cynthia and your choice of dialga, palkia, or giratina. You can only choose one so choose wisely. Each will have their respective orbs(dialga-adamant, palkia-lustrous, giratina-gresious) but this is the only way to get giratina's origin form in heart gold without cheating because the gresious orb is not tradable.
Don't stop here... Check out our complete collection of Pokemon Heart Gold cheats
Comments for this hint