You have to trade it! (i know it sucks but u can trade back!...)
Haunter at level 25
Haunter can level up and evolve. It evolves by trading with another player.
Gastly evolves at level 20 into Haunter
You don't level him up, you trade him with someone.
You have to trade the Haunter to evolve. I learned the hard way. It got to level 59 and I traded..... it evolved!
Gastly evolves into Haunter once it reaches level 25 or higher.
There is no need to trade to evolve Haunter in Light Platinum, the Pokémon Ruby hack. It will simply evolve as you level it up.
Ok just stop lvling up you trade your haunter. Then it volves into gengar
Gastly evolves once it reaches level 18. It evolves into a Haunter. To evolve Haunter into a Gengar, you must trade it to another player.
Gastly evolves at level 22 then Haunter evolves by trading it.
You will need to level up Haunter to level 50 to evolve it in Pokemon Resolute.
No it won't Haunter only evolves when you trade across to a similar game, you have to trade it to Leaf green for it to evolve. It will migrate to Pokemon platinum and will stay as a haunter. To evolve it to a Genger on platinum, you must trade it to another platinum, diamond or pearl