Pokémon +

Type Effectiveness
Ghosts are well-known for being invulnerable to Fighting and Normal attacks, but in return, Ghost type attacks have no effect on Normal.
Ghost type Pokémon are also partially resistant to Bug and Poison attacks, but are weak to Dark and their own Ghost attacks.
Ghost attacks are super effective against Ghost Pokémon (That's right!) and Psychic, but are not very effective against Dark and Steel.

Ghost Pokémon's main use is to take down Fighting, and sometimes Psychic, Pokémon.

An interesting note is that Ghost's weaknesses are covered by Dark type, and vice versa, meaning a Ghost/ Dark Pokémon has no weaknesses.

Attacks
There aren't many Ghost type attacks, and contrary to what I assumed before writing this, they're mostly Physical type attacks.
Shadow Force has an impressive 120 power, and can even punch through Protect. Similar to Fly, it takes a turn of hiding to charge up, though. It's exclusive to the legendary Pokémon, Giratina.
Night Shade, a classic Ghost-type move, offers damage equal to the user's level at 100% accuracy. It's also one of only three Special-type Ghost moves.
Shadow Ball is another Special attack, woth 80 power and a chance at lowering the enemy's special defence.

The non-damaging moves are what's really special about Ghost Pokémon, though. Confuse Ray does exactly what it says on the tin- confuses. Destiny Bond is for when you know you're about to get pwned-if you go down that turn, your opponent's Pokémon is KO'd along with you. Nightmare on its own is a non-damaging move, but if your opponent is sleeping, say by Hypnosis, you're laughing.

Some damaging moves have status problems, such as It isn't a Ghost Attack, but a Ghost's worst fear is Odour Sleuth- a normal move which allows any attack to land on a Ghost.

Oh, and Curse. Curse is a "???" type move, but is special for Ghost Pokémon- for them, it cuts the user's HP, but effectively poisons the foe, but with about five times as much effect as poison. For other Pokémon, it just lowers the speed and raises Attack and Defence.

Pokémon

Mismagius really looks like it should be an evolution of Honchcrow, but it's actually a pure Ghost type that evolves from Misdreavus. Its SpA, SpD, and Speed are all at 105 as standard, while its HP and physical stats are a less desirable 60.


Dusknoir is very impressive defensively, offering 130 in both Special and Physical defence. Awful apart from that, though. At least he reminds me how to say "Black" in French. I seriously can't speak French, even after four years.


Gastly, Haunter, and Gengar were the only Ghost Pokémon in the first generation, and are now the type's most memorabe family. They're part Poison, though.


Drifblim and its pre-evulution, Drifloon, are Ghost/ Flying Pokémon introduced in Diamond and Pearl. Their types give them a lot of weaknesses, but they have masses of HP.


Spiritomb is Ghost and Dark, and therefore has no weaknesses. You can hear the wonderguard hax0rs coming... Actually, you can't, but it's an interesting Pokémon to have.


And here is the wonderguard. Shedinja only has 1HP, but can only be taken down by attacks that are super effective against it-Dark, Fire, Flying, Ghost, and Rock. If you don't have at least one of those types in your team, you're in trouble. I don't get how it attacks when it's supposedly just an empty shell, though...


Sabeleye is another Ghost and Dark type. Look into its eyes and it will steal your SOULS. NEED MORE SOULS!
Went a bit Nightmare there, I'm afraid.


Froslass, AKA my baby, is Ice type, meaning it's instantly good enough to get into here.

Legendaries

Giratina is one of Diamond and Pearl's masses of legendaries. Its speciality is the amazing "Shadow Force" move. It appears in cemeteries and lives in a reverse world of ours, and... HAS TEH UBA STATS