How Do I Evolve a Haunter in "Pokemon: Shinygold"?by Matthew Anderson ; Updated September 22, 2017
In all official “Pokemon” games, Haunter evolves into Gengar when it is traded to another player. There is no level or item requirement for this evolution to occur. “Pokemon: ShinyGold” is a mod of “Pokemon: FireRed.” Due to it being a mod, it is impossible to trade with other “Pokemon” players when it is used. This normally would prevent Pokemon, such as Haunter, from being able to evolve. To address this issue, the mod creator added alternative leveling paths for these Pokemon.
Go to the area with the highest-level random Pokemon you have reached.
Move Haunter to the first position in your Pokemon roster. This makes him the default choice when a battle starts.
Wander around the area until you start a random encounter.
Switch to your most powerful Pokemon.
Defeat the random encounter. The experience is divided between Haunter and the Pokemon you used to defeat your opponent.
Repeat Steps 3 through 5 until Haunter reaches level 42. Haunter evolves as soon as it reaches level 42.
Haunter does not evolve when he reaches level 42 in any other “Pokemon” game. This is a unique requirement of the “Pokemon: ShinyGold” mod.
You can use Haunter to directly defeat opponents, but this is usually a less practical approach. Haunter’s damage abilities are, by default, very limited until he evolves into Gengar. You can teach him more attack options with items, but most players may not want to waste the item to add to an attack that is most likely going to be replaced with Gengar’s more powerful moveset.