Use Psychic, Ghost and Dark attacks. (Those are super effective)
Don't use Ground attacks because Gengar has an ability called levitate which renders all ground attacks useless.
For more information, look here:
http://www.serebii.net/pokedex-dp/094.shtml
Don't use Ground attacks because Gengar has an ability called levitate which renders all ground attacks useless.
For more information, look here:
http://www.serebii.net/pokedex-dp/094.shtml