Trade it from Pearl, Diamond, or Platinum.
Chat with our AI personalities
In Platinum, you must talk to the sailor in Canalave City and he says his son is having bad dreams. You can have him take you to Full Moon Island, which Cresselia is inhabiting. When you get to the clearing where Cresselia is in, it will escape and start roaming Sinnoh. You can find out where it is using the Poketech. When it dissapears, it will drop the lunar wing. You cannot get the lunar sing in Soul Silver.
If Cresselia disappeared off of your map completely, then you have already caught Cresselia, or there is a glitch in your game where Cresselia has just disappeared off of your map. Further details would be needed for a more in-depth assessment as to why this has happened if neither of the two reasons stated are why Cresselia isn't on your map.
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no you do not
darkrai