What plates do you need to catch Arceus

None. you don't need any plates, but you do need an item called Azure Flute. play it where you caught Dialgia or Palkia. bring at least one lv. 100 Pokemon with you. does not matter what type. he is lv. 70, and is tough. bring lots of timer balls. i recommend using a Action Replay to get the flute. Good luck catching Arceus!