How to get a Gengar in platnuim with out trading

You may think that to get a Gengar you need to trade. But that's not true!!! What you need is any Pokemon Gameboy advanced game. Insert the game in while the DS is off. Then turn it on and go to the Old Chateau. then go to the room with the purple painting in it. Do not be scared if a ghost appears in the room next door. It won't hurt you. Then walk around in the room. Sooner or later, You will find a Gengar! Note: The chance of finding a Gengar by doing this is very low. So it will take some time ( I only encountered two in an hour). And don't call me a lair until you try it your self!