How do you get Arceus in pearl with mystery gift not at a Nintendo event?

Hope this helps-First, you have to get the red, green, and yellow shards. When you get all, of them, migrate one Pokemon with one shard(in leafgreen or firered). If you have all the shards, you should save and turn it back on, now you have a Flute(first Word starts with a)Then you migrate a different Pokemon to diamond/pearl and have the flute on that Pokemon. Then go to where you catch Dialga/Palkia and play the flute. Stairs will appear. Make sure you're ready, then go up them, and Arceus will be waiting.

(This is after beating the Sinnoh Dex and the Pokemon League.)