Pleas help I forgot wer the Pokemon mansion is and I need a cresalia badly..

The mansion is just south of Hearthome and you find Cresselia on Full Moon island after getting the National Dex. Just talk to the sailor in Canalave City that took you to Iron Island

Cresselia is found on Fullmoon Island, not Pok�mon Mansion. You can go to Fullmoon Island after you get the national dex (and beat the champion) by going to Canalave City and talking to the sailor who took you to Iron Island in the past. Cresselia will run and you will have to follow it much like Mespirit.

Cressilia is when you beat the Poke'mon League. Go to Canalave City, and go into the sailors house south of the Pokemon Gym. Talk to his wife, and she'll say that he's sick. Talk to the sailor now, and you'll unlock a new place to go. Go to Newmoon Island, and go into it's woods. Cressilia will be there, but will feld, leaving a feather. Cressilia should be just like Mesprit, and it fleds in battle. You'll need to use either Mean Eye, or use a Masterball on it.

The Pokemon Mansion is south of Hearthome City, by the area in which you entered it for the first time. Keep going south, and you should run into it (Kinda hard not to miss).

The Pokemon mansion is south of hearthrome in other words down and you get cresselia when you beat the elite four and complete the national dex. You go to canalave city and go to the sailors house he will then take you to an island where cresselia is at

You don't find cresselia in the poke'mon mansion you find him on new moon island(ask the man that takes you to iron island and he will take you there after you have the national poke'dex you have to chase him/her like mesprit)