How do you get Arceus cursed form?

Arcus doesn't have a cursed form but if you give it a dread plate its type changes to dark type. If you give it a spooky plate its type changes to ghost type.

that is not true there is a curse form programed into the game copy and paste this link to see the info on serebii http://www.serebii.net/diamondpearl/arceus.shtml

First off, it isn't "cursed" form of any sort. It's ??? form. A form of Arceus isn't named after a move of any sort (he's not called "Flame Wheel-Form" in Fire-Form, is he?), it's named after the type. And Curse's "type" is ???.

Secondly, there isn't a way to get him. While this seems sort of stupid, the real reason the Sprite is there is to prevent the game from crashing, in case anyone were to hack a ???-type plate for him to hold. They probably found the sprite by looking through the game's files.

And no, using Roost on a Flying-Form Arceus won't make him ???-type. :P It just makes him typeless, without any weaknesses or resistances. ~vaati000