FireGround
Fire and Ground types: weaknesses, resistances and Pokémon
Fire and Ground Pokémon take quadruple damage from Water moves, take double damage from Ground moves, resist Fire, Poison, Bug, Steel and Fairy moves and are immune to Electric moves.
With 6 resistances and immunities against 2 weaknesses, it is a very solid defensive combination.
Fire moves are super effective against Grass, Ice, Bug and Steel and not very effective against Fire, Water, Rock and Dragon. Ground moves are super effective against Fire, Electric, Poison, Rock and Steel and not very effective against Grass and Bug.
To beat these Pokémon, your best pick is Water moves. Avoid Fire, Poison, Bug and Steel moves, which deal little or no damage.
There are 2 Pokémon with this combination, such as Numel and Camerupt.