Happiny
say yes to all of his answers
go to the Pokemon mansion and go left and there is a door. go in the door and talk to the guy in the purple suit.hes the guy who owns the mansion.
NO
go to the Pokemon mansion talk to mr. blacklot the guy who owns the mansion go there every day he'll tell you about a rare Pokemon there is over 10 different Pokemon eventualy it will be a eevee
cach pearl the legndary Pokemon
u hav to get the national pokedex then go to the mansion where the guy love his garden and on certain days hee will tell u "mew is in the garden"
You can't actually catch it in Pokemon platinum/pearl/diamond but you can see it by going to Pokemon mansion(route 212). Go to first room on right and talk to old guy. He'll show you a book which has manaphy in it.
Pastoria
The master of the Pokemon Mansion tells you which Pokemon you can find in his garden. Some Pokemon, like Meowth, can only be found in that garden. Each day another Pokemon appears...
be more spcific
NO HE CANT.
after the guy says to tell that one guy to say hey or what ever u have to go talk to him and go back into the cave where he got the treasure