I don't know if this has been posted before, but there is a glitch in some Japanese Diamond/Pearl versions that allows you to catch Darkrai and Shaymin, which would normally only be available by a Nintendo Event. You could also use it to skip the Elite Four.
Here it is, if anyone wants to know more. It works for both Diamond and Pearl though.
GameFAQs: Pokemon Pearl (DS) Elite Four Door Glitch Guide by L255J
If you happen to have an early Japanese Diamond/Pearl version and want to try it, you should read and do EXACTLY what the guide says, or risk corrupting your game.