"Gastly is largely composed of gaseous matter. When exposed to a strong wind, the gaseous body quickly dwindles away. Groups of the Pokemon cluster under the eaves of houses to escape the ravages of wind."
Gastly is the original Ghost-Type Pokemon, and has endured for quite some time because of it. It also has one of the coolest intro sounds when you find it in a battle or in the wild. Whether in game or in the anime, Gastly is not to be underestimated.
Gastly's Basic Attacks are Sucker Punch and Lick, while its Special Attacks are Sludge Bomb, Dark Pulse, or Omnious Wind.