FireGrass
Fire and Grass types: weaknesses, resistances and Pokémon
Fire and Grass Pokémon take double damage from Poison, Flying and Rock moves and resist Grass, Electric, Steel and Fairy moves.
The balance is even: 3 weaknesses and 4 resistances or immunities.
Fire moves are super effective against Grass, Ice, Bug and Steel and not very effective against Fire, Water, Rock and Dragon. Grass moves are super effective against Water, Ground and Rock and not very effective against Fire, Grass, Poison, Flying, Bug, Dragon and Steel.
To beat these Pokémon, your best pick is Poison, Flying and Rock moves. Avoid Grass, Electric, Steel and Fairy moves, which deal little or no damage.
There is 1 Pokémon with this combination, such as Scovillain.