Dark and ghost-type attacks are the most effective attacks to use against ghost-type Pokemon, such as Gengar and Shuppet. On the other hand, fighting and normal-type attacks generally have no effect at all against ghost types.
There are 44 ghost-type Pokemon, as of February 2015. In some case, these ghost-type Pokemon can have a secondary element, such as fire, water, electric, ice, poison or bug. The secondary type will affect a Pokemon's strengths and weaknesses. For example, Shedinja, a bug and ghost-type Pokemon, is also weak to fire, flying and rock-type attacks, in addition to dark and ghost-type moves.