GrassGhost
Grass and Ghost types: weaknesses, resistances and Pokémon
Grass and Ghost Pokémon take double damage from Fire, Ice, Flying, Ghost and Dark moves, resist Water, Grass, Electric and Ground moves and are immune to Normal and Fighting moves.
The balance is even: 5 weaknesses and 6 resistances or immunities.
Grass moves are super effective against Water, Ground and Rock and not very effective against Fire, Grass, Poison, Flying, Bug, Dragon 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 Fire, Ice and Flying moves. Avoid Water, Grass, Electric and Ground moves, which deal little or no damage.
There are 10 Pokémon with this combination, such as Phantump, Trevenant, Pumpkaboo and Gourgeist.