It evolves into Haunter at Level 25.
Level 25
Gastly evolves at Level 25.
Gastly evolves to Haunter at level 25. Then, Haunter evolves into Gengar by being traded.
Gastly evolves into Haunter at level 25 and then into Gengar when you trade it to another game.
gastly evolve on level 25
Gastly evolves at level 25.
To evolve Gastly into Haunter just get it up to level 25.
Gastly evolves into Haunter at level 25, then trade it and it will evolve again into Gengar.
Level 25
Gastly evolves at level 20 into Haunter
Gastly evolves at LV. 25
Gaspar is not a pokemon. If you meant Gastly than between lvl 18 to 20.