Ghost-type Pokémon

Pure Ghost-types

Immune to Fighting and Normal attacks; strong against Bug and Poison attacks; weak against Dark and Ghost attacks
Misdreavus

Ghost/Poison-types

Immune to Fighting and Normal attacks; strong against Bug, Grass and Poison attacks; weak against Dark, Ghost, Ground and Psychic attacks
Not strong against Bug attacks in Red, Yellow and Blue Versions
Gastly
Haunter
Gengar