you have to trade from another game
You can't catch a Haunter in Emerald. You can trade for one, you can find a Duskull/Dusclops at MT Pyre, but you can't straight out find a wild Haunter.
In Pokémon Pearl, in order to catch Gengar you can find wild Gastly in Lost Tower and Old Chateau and then after catching one you can raise it until it reaches Level 25 at which point it will evolve into Haunter and then you can trade Haunter to another trainer in order to evolve it into Gengar and then you can catch wild Haunter in Turnback Cave and you can only catch wild Haunter in Old Chateau in the event of Ruby, Sapphire, FireRed, LeafGreen or Emerald inserted into the Gameboy Advanced slot and then you can evolve Haunter into Gengar by trading Haunter to another trainer.
The way to evolve Haunter has been, and will always be, by trading. If you have a Haunter in Pokemon Emerald trade it to Sapphire, Ruby, Fire Red or Leaf Green and make sure he isn't holding an EVERSTONE as that will prevent its evolution.
No you must trade from FireRed and LeafGreen
You cant. You have to catch a gastly then envolve it to haunter then trade with someone and trade back haunter will envolve to gengar!
yes
you have to catch a haunter or something else.
There's a 30% chance you can catch a level 19 Haunter in the grass on Route 8 at night. You can also catch level 16 or 17 Haunter in the forest region of the Johto Safari Zone at night.
To get a Gengar you must first catch a Haunter. To evolve the Haunter you have to trade it to another gaming system.
In the safari zone dessert area
yes into a haunter and the trade it to evolve into a gengar
No you cannot catch Celebi in Pokemon Emerald.