There are only two Ghost moves that cause damage, Night Shade and Lick. The former does set damage based on the user's level, the latter sucks, and both have no type advantage against anything. The right way to use a Gengar is not by using Ghost moves. Gengar's still a good pokemon nevertheless. --- gbchaosmaster
On a side not through Ghost aren't really that valuable in an offensive line-up but for the defense they can wow you. They are completely immune to normal and fighting attacks and that covers a lot of moves man.
Problem with that is, in this gen, and all since, no serious trainer has just one type of moves on any of their normal type pokemon, and fighting types were almost never used (and even they often had Rock Slide or another move that WOULD hit ghost types for a lot).
This means that all properly taught pokemon will be able to hit ANY type of pokemon. --- User is finally online...
gengar also has great special, and since there is no special split he takes very little damage from many pokemon. Stuff like persian and weezing can't do very much to him and pokemon like pinsir are completely unable to harm him. Gengar's great special allows him to do some good damage with thunderbolt and mega drain (and possibly psychic and explosion). --- If you don't look at this video, you will go the rest of your life wondering what it is. http://www.youtube.com/watch?v=5uZr3JWYdy8