You don't need to cheat to get a ditto. You wait till you get the national pokedex and the pokeradar and go to the route right next to canalave city. You should be able to get a ditto pretty fast.
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well in Pokemon platinum you can just get the member card and get darkrai after getting darkrai you can get cresselia
Breed Ditto and Manaphy. Ditto + Manaphy = Phonie Ditto + Phonie = Phonie
you could just get a trade for ditto.
The Trophy Garden is the only place to get Ditto in Pokemon Platinum, without trading or cheating of course.
you can catch a Ditto if you talk to Backlot every day for a long time. He will say that he saw a ditto there. Then, you can catch a ditto in the trophy garden.