Go to an area where Jigglypuff can be caught, or you could see the man at Pokemon mansion and he'll tell what kind of Pokemon he saw in his garden (everyday its a different Pokemon so you may have to check once a day to see what Pokemon he's seen), or if you've beaten the game mirgate your Jigglypuff from another Pokemon GBA and go to pal park to catch them. afterwards the man at the front desk will ask if you want your Pokemon sent to your PC boxes and you say yes. And there you have your Jigglypuff. (use a moonstone to evolve it into Wigglytuff if you want too).
Chat with our AI personalities
at trophy garden Baclot will say a jigglypuff gave him a smooch on the cheek.It will take a while ,but you will find one eventually
You can find a few on route 3.
neither of them is better, they are both the same, but in diamond, you catch dialga, and in pearl, you catch palkia, and you can catch different Pokemon in each game for example: you can catch this Pokemon in diamond, but not pearl but: you can catch this different Pokemon in pearl, but not diamond
You can catch makuhita in the fighting area in Pokemon diamond
at the Pokemon mansion after obtaining nat dex talk to mr backlot