Then trade haunter to evolve into gengar. You can also catch a gengar at the Old Chateau
in Eterna Forest in the 5th room on the second floor. You have to have any of the old GBA
games inserted into the dual slot

you have to have gba in bottom

room with the picture that seems to be watching you so you just have to walk around until
you find Gengar or you can trade a Haunter for another Haunter and it will evolve right
after you traded it but it has to be fron another game

can't get a Gengar when you trade Medicham for a Haunter in Snowpoint City when that girl
asks to trade with you