I had complete my answer to you,and after that I realized something .. I was remembering Mew was the legendery that you need to talk to his statues in 2 forests .. But that was Celebi ...
So i gues i will not have any problem when i caught him :D
I m really sorry for spending your time
Ty for your help and your time :D
PS: One more thing .. I found a video that you catch Palkia.It exist only in the "second" version ? ( the one with bigest pokedex)