The quickest way to revert Shaymin is to put it into the PC. However the other ways are wait until night or freeze Shaymin.
Chat with our AI personalities
open your menu go to Pokemon select shaymin pres A then go to ITEM then choose put back or something then he will transform back to normal
Actually just wait until night without shaymin holding the flower thing
Sorry, but Shaymin can only change form in Platinum.
You can't change Shaymin into Sky Form in Pokemon Diamond (that includes pearl). You can only change Shaymin into Sky Form in Pokemon Platinum (that includes Heart Gold and Soul Silver). You can get the Gracidea to change Shaymin into Sky Form.
only if in was a event shaymin and you traded it Jrskirbybob- I will try and get back to you on that