You give it to Arceus to change its stats and type.
go underground at route 220 and dig it out
It is located in Route 220, on a small island, and there is not much more I know about it.
under ground
You can search on youtube. that's where i found mine.search Pokemon PLatinum plate locations.
In the Underground
there isn't a aqua plate it is a splash plate, you find it underground
the splah plate is to up water pokemon's moves and make them stronger
there is no such thing as a "Curse Plate."
i have heard that splash only works if you are holding a water plate
head past the two girl swimmers on route 220, and you will see a poke ball. it's the splash plate
Underground!
battle them half of them probably only have splash