This action replay code features the Arceus event for Pokemon HeartGold and SoulSilver.
1. Make sure that you have a useless Pokemon on your first slot in your party.
2. Use an action replay for DS if you wanted to place it on a DS.
3. Press L+R
1. Make sure that the Arceus is in the first slot in your party.
2. Leave all other 6 slots in your party blank.
3. Go to Ruins of Alph. Main requirement is that you solved all of the Pokemon puzzles.
4. Go to the observatory. Watch it happens right in front of your eye.
This will give you Pokemon #496 Arceus, which has the game detail coming from the Hall of Origins in Sinnoh region of Pokemon Diamond. Level 80, has hasty nature, knows Hyper Voice, Hyper Beam, Earth Power and Recover. Maximum EV, IV, Contest stats and has normal rank for cute contest. Caught in Cherish Ball.