Ice/fire/rock/water/eletrick or physic arceus
You need arceus event
the reason why it won't work is because you need the event arceus from diamond or pearl.
yes it exists but to get it you need a Pokemon event
Arceus cannot be found during normal gameplay. You need to get it from an event
You need the azure flute
There is no event where you can catch Arceus, you just interact him in the Hall of Origin, but you need to blow on the Azure Flute
No, you do not need to complete your Pokedex. You have to do a Wi-Fi event. However, all of the events regarding Arceus have already passed.
No, you do not need all of the plates to catch Arceus. You can use the plates to change Arceus' type, though. Arceus is only available by event (which has long since passed). You can also use an AR (action replay) to hack the game and get an Arceus, all without plates.
no you can use any as long it is a special event one
you need the action replay or a Nintendo event.
You cannot get it in an egg, you need to get the Azure Flute in Pearl/Diamond/Platinum from an event/Action Replay. Plus, you need the event Arceus to activate the Palkia/Dialga/Giratina event anyway.
Arceus is an event only pokemon. You need to wait for Nintendo to do a new event where you can get it over WiFi, or hack your game with Action Replay.