cerebi.net says its in the old mansoin-mitonga island-dining room but you need to first go to tilt village and go to the nearest house to mitonga road (west) and go in. the lady informs you that she yelled at her purugly for breaking one of her favorite antique plates and it ran away. then she tells you to go look for the missing purugly. a man asks you whats wrong and you tell him then he tells you he saw a missing purugly that was crying and it looked sad. then you go to the mansion dining room and purugly should be there.
You can only transfer the Manaphy egg. Get the Manaphy egg code and then link the games up wirelessly and transfer it. Then go to any poke mart and talk to the green man with the hat on. He will give you the egg that you sent over. Hope this helped!!!!!!!
Is mission 3 the one with the grimer? Try to avoid other Pokemon than grimer or necessary like raticate and tangela and keep on trying!
when it is on the ground do a quick loop and it will fly. capture it while it is flying