PoisonGhost
Poison and Ghost types: weaknesses, resistances and Pokémon
Poison and Ghost Pokémon take double damage from Ground, Psychic, Ghost and Dark moves, resist Poison, Bug, Grass and Fairy moves and are immune to Normal and Fighting moves.
The balance is even: 4 weaknesses and 6 resistances or immunities.
Poison moves are super effective against Grass and Fairy and not very effective against Poison, Ground, Rock and Ghost. Ghost moves are super effective against Psychic and Ghost and not very effective against Dark.
To beat these Pokémon, your best pick is Ground, Psychic and Ghost moves. Avoid Poison, Bug, Grass and Fairy moves, which deal little or no damage.
There are 4 Pokémon with this combination, such as Gastly, Haunter, Gengar and Pecharunt.