Prior to Generation VI, Pokémon that are both Dark-type and Ghost-type have no weaknesses (excluding Fighting-type moves used under immunity-negating conditions such as Ring Target or Scrappy), as the resistances of the Dark type cover the weaknesses of Ghost, and vice-versa. In Generation VI, the Fairy type was introduced, which is super effective against Dark and not resisted by Ghost, so these Pokémon now have a weakness to Fairy.
Ghost types are also unique in the fact that they have a type-specific attack: Curse, which, other than being the only ???-type move before the type was removed in Generation V, works differently for Ghost-type Pokémon than it does for other Pokémon.
Contrary to Dark-types, most Ghost-type Pokémon are special attackers due to their typically high Special Attack, despite the fact that Ghost-type moves were physical moves prior to Generation IV. In Generation I, there were no types that resisted Ghost-type moves, although there was only one move that would be affected by same-type attack bonus and due to a possible error Psychic-type Pokémon were immune to Ghost-type attacks. In Generation II, Steel and Dark were added in order to resist Ghost-type moves. As of Generation VI, the only differences between Dark and Ghost is that Dark-type moves are not very effective on Fighting or Fairy while Ghost-type moves do normal damage to those types, and Ghost-type moves do not affect Normal Pokémon.
Ghost-type moves are great for neutral coverage, as Steel-type Pokémon no longer resist them in Generation VI. No Pokémon resists a combination of Fighting and Ghost-type moves, as the only combination capable of this (Normal/Ghost) has never materialized. A combination of Fairy and Ghost-type moves has nearly as good coverage, only resisted by Normal types with a secondary type that resist Fairy, of which there are currently onlytwo. Despite this, there are few high-power damaging Ghost-type moves.
In Contests, Ghost-type moves are typically Clever moves, but some may be any of the other Contest conditions.
As of Generation VII, there are 46 Ghost-type Pokémon or 5.7% of all Pokémon (counting those that are Ghost-type in at least one of their forms, including Alola Forms), making it the 2nd rarest of the eighteen types, only above Ice.
Generation VII introduced the most Ghost-type Pokémon of any generation, with eleven, and Generation II introduced the fewest Ghost-type Pokémon, with only one.
Generation VII introduced the most Ghost-type moves of any generation, with eight, and Generation V introduced the fewest Ghost-type moves, with only one.
In Generation I, Ghost-type moves have no effect on Psychic-type Pokémon, though an abundance of evidence suggests that this may have been an error. Multiple sources mention that Ghost-type moves are super effective on Psychic-type Pokémon: official strategy guides published by Nintendo, two episodes of the anime (The Tower of Terror and Haunter versus Kadabra), and even the games themselves, where a Trainer in the Saffron Gym mentions that Psychic-type Pokémon "only fear Bugs and Ghosts" (though the reference to Ghost-type Pokémon was removed in Pokémon Yellow). This was corrected in Generation II to make Ghost moves actually be super effective against Psychic-type Pokémon.
There are no Ghost-type moves with an accuracy lower than 100%.
While the Ghost type has an immunity to Normal-type moves, several damaging moves that display as Normal can affect them, including Hidden Power (whose actual type varies) and Struggle (Generation II onwards).
From Generation VI onward, it is not possible for any Pokémon to possess a double resistance to Ghost. The only Pokémon to possess a double resistance in previous generations are Pawniard and Bisharp, both of which are Dark/Steel.
The Ghost type is the only type immune to two types: Normal and Fighting.
It is also the only type to have ever been ineffective against two types: Normal and Psychic in Generation I.
In Pokémon Conquest, Ghost-type Pokémon which are not part-Flying or have Levitate are shown with an animation of physically passing through enemies, referencing the common belief that real life ghosts can pass through solid objects. They cannot, however, pass through any other obstacle on the field in-game.