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Shiny Geodude is cool cos it looks like a lump of gold instead of rock.
Shiny Ponyta is cool cos it has blue flames and shiny Rapidash's flames look like smoke.
I also like shiny Castform...a lot =)
This happened to me, and it was because the internal battery had become disconnected. This was a problem among many peoples games after about 5 or 6 years of gameplay. It can be fixed, of course, but its hardly worth the bother; it's cheaper and easier to just buy a new game.