Ghost and Steel types: weaknesses, resistances and Pokémon
Ghost and Steel Pokémon take double damage from Fire, Ground, Ghost and Dark moves, resist Bug, Grass, Ice, Flying, Psychic, Rock, Dragon, Steel and Fairy moves and are immune to Normal, Fighting and Poison moves.
With 12 resistances and immunities against 4 weaknesses, it is a very solid defensive combination.
Ghost moves are super effective against Psychic and Ghost and not very effective against Dark. Steel moves are super effective against Ice, Rock and Fairy and not very effective against Fire, Water, Electric and Steel.
To beat these Pokémon, your best pick is Fire, Ground and Ghost moves. Avoid Bug, Grass, Ice and Flying moves, which deal little or no damage.
There are 4 Pokémon with this combination, such as Honedge, Doublade, Aegislash and Gholdengo.