Gastly is unobtainable in Pokemon Ruby. You need to trade one from Pokemon Firered or Leafgreen.
Go to lavendar town and then enter Pokemon tower in there you can find a gastly.
Gastly is found in Bellsprout Tower.
No, Gastly cannot learn to fly.
Gaspar is not a pokemon. If you meant Gastly than between lvl 18 to 20.
Gastly evolves to Haunter at level 25.
Gastly evolves at Level 25.
Gastly and Misdreavus on pearl. Gastly and Murkrow on Diamond.
Yes you can get gastly I dont no about duskull
Gastly evolves at level 25.
Gastly evolves at level 20 into Haunter
Gastly Lvl.25>Haunter Trade>Gengar