PoisonPsychic
Poison and Psychic types: weaknesses, resistances and Pokémon
Poison and Psychic Pokémon take double damage from Ground, Ghost and Dark moves and resist Fighting, Grass, Poison and Fairy moves.
The balance is even: 3 weaknesses and 4 resistances or immunities.
Poison moves are super effective against Grass and Fairy and not very effective against Poison, Ground, Rock and Ghost. Psychic moves are super effective against Fighting and Poison and not very effective against Psychic and Steel.
To beat these Pokémon, your best pick is Ground, Ghost and Dark moves. Avoid Fighting, Grass, Poison and Fairy moves, which deal little or no damage.
There is 1 Pokémon with this combination, such as Munkidori.