PsychicGhost
Psychic and Ghost types: weaknesses, resistances and Pokémon
Psychic and Ghost Pokémon take quadruple damage from Ghost and Dark moves, resist Poison and Psychic moves and are immune to Normal and Fighting moves.
The balance is even: 2 weaknesses and 4 resistances or immunities.
Psychic moves are super effective against Fighting and Poison and not very effective against Psychic and Steel. Ghost moves are super effective against Psychic and Ghost and not very effective against Dark.
To beat these Pokémon, your best pick is Ghost and Dark moves. Avoid Poison, Psychic, Normal and Fighting moves, which deal little or no damage.
There are 2 Pokémon with this combination, such as Hoopa and Lunala.