GrassPoison
Grass and Poison types: weaknesses, resistances and Pokémon
Grass and Poison Pokémon take double damage from Fire, Ice, Flying and Psychic moves and resist Grass, Water, Electric, Fighting and Fairy moves.
The balance is even: 4 weaknesses and 5 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. Poison moves are super effective against Grass and Fairy and not very effective against Poison, Ground, Rock and Ghost.
To beat these Pokémon, your best pick is Fire, Ice and Flying moves. Avoid Grass, Water, Electric and Fighting moves, which deal little or no damage.
There are 14 Pokémon with this combination, such as Bulbasaur, Ivysaur, Venusaur and Oddish.