There is no Unknown Plate for Arceus, there are only plates for each type.
i do not think there is a code try codejunkies.com if it is not there i do not know where to find it...
Arceus is a Normal-type Pokémon but if you give it plates to hold it will change its type to the plate's type.
There isn't one you have to get items you don't need in your bag and use the item code.all the plates ( except the rumored ??? type plate ) are listed.
to change it's type. (splash plate=water type,etc)
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.
You get them through out the game
If you have Arceus, then all you have to do is give it one of the plates that can be collected around Sinnoh, for example, the Splash Plate. Then the Arceus will change its type.
you ned to go to www.codejunkies.com
there is none
There is no Unknown Plate for Arceus, there are only plates for each type.
No, but it helps if you do catch it. Arceus has a special ability called Multitype. When it holds a plate, it transforms into that plates preferable type. (E.g. Stone Plate = Rock Type, Zap Plate = Electric type). it is not proven when you get all of the plates arceus will appear, but what you really need the azure flute.
no you must have plates ex: thunder plate or sky plate
If we are talking Game I don't know. Maybe Arceus since he can use a plate to use super effective moves against psychic type like mewtwo. If we are talking Anime Arceus. In the anime if Arceus has all life plates he is invulnerable.
On the S.S.A Aqua.
i do not think there is a code try codejunkies.com if it is not there i do not know where to find it...
the plates can be given to Pokemon to boost certain moves, but there is an alternative purpose. there is an uncomfirmed Pokemon(although it kind of is since you can catch it thanks to action replay) known as Arceus, it's supposedly the creator of all Pokemon and you would use the action replay card to get an azule flute that guides you to Arceus' lair were you fight and possibly catch it. anyway, when you catch Arceus it has a statistic of normal, if you give arceus any of the plates, it will change the stat of arceus to whatever the plate is, if it's a spooky plate it becomes ghost, the colour of arceus changes along with the stats of it too