At Turnback Cave
haunter
Haunter learns Payback at Level 28 in "Pokémon Platinum."
You have to trade the Pokemon to evolve it.
You have to trade it and it evolves.
Ask a friend to trade u a Pokemon for his/her haunter
gengar haunter gastly
you cant you have to evolve haunter
Haunter at level 25
Haunter can level up and evolve. It evolves by trading with another player.
Gastly evolves into Haunter once it reaches level 25 or higher.
in victory road
Ok just stop lvling up you trade your haunter. Then it volves into gengar