Instructions
Fly to Jublife City and go to the Jublife TV center. Ascend the stairs to go to the second floor. Talk to the male non-player character who is wearing glasses. Answer him with the two following phrases: "Everyone happy" and "Wi-Fi connection." Since you know the magic words, he will activate the mystery gift function for you.
Restart "Pokemon Platinum." On the main menu of the game select "Mystery Gift," which is the third option. If Nintendo is offering the azure flute via Wi-Fi, choose the "Get Via Nintendo Wi-Fi Connection" option. Your game will download any items that Nintendo is offering through Wi-Fi. Pick up the azure flute at any PokeMart in Sinnoh.
Capture a Rock- or Fighting-type Pokemon. Give the creature rare candies until it is Level 80. Teach the Pokemon rock- or fighting-type moves. Arceus is weak against rock- and fighting-type moves. Go to the PokeMart in Blackthorn City and buy 50 to 100 ultra balls.
Ascend the ladders and stairs in Mt. Coronet to reach the peak. At the peak of Mt. Coronet, you will reach spear pillar. The game will prompt you to choose whether to blow into your azure flute. Choose yes to blow into it. After you blow into the azure flute, a staircase will appear.
Ascend the lengthy staircase. Walk up to Arceus and save your game. Press "A" to battle the Level 80 Arceus. Lower its hitpoints with your Level 80 rock- or fighting-type Pokemon. You will probably use 25 to 50 ultra balls before you capture the Arceus.