Route 8
Safari Zone (Nighttime)
Evolve a gastly that you can catch in the sprout tower
Haunter evolves by trade
Trade Haunter and you will get a Gengar.
Via trade.
Haunter does not evolve into Gengar at a certain level. Haunter needs to be traded to another player. Once he is traded, he will evolve.
Ghastly evolves into Haunter at level 25. Then Haunter evolves by trading.
Kadabra, machoke, haunter 'Just trading' - Kadabra; Machoke; Graveler; Haunter.
forest at night
You trade it at a high enough level
pewter city.
Trade it to a friend take it back it will be a gengar now.
you can't find haunter in Black