You have to breed a Jigglypuff/Wigglytuff with a Ditto or a male Pokemon in the Fairy Egg Group. There is no incense needed here. Also, in HGSS, you can get one in the Amity Meadow Pokewalker course and in DPP, in the Trophy Garden (Rare %5), after Mr. Backlot makes his butler add it to the garden (talk to him, also there won't be a 100% chance of him adding it) . In Platinum, it will be encountered at level 22, and in Diamond/Pearl, 16-18. On any given day, the "planted" Pokémon (Igglybuff) that was in the Trophy Garden the previous time Mr. Backlot was last spoken with will also still be there, allowing a two-day window to catch each of these Pokémon.
Hope I helped! :)