Fire and Steel types: weaknesses, resistances and Pokémon
Fire and Steel Pokémon take quadruple damage from Ground moves, take double damage from Water and Fighting moves, resist Grass, Ice, Bug, Steel, Fairy, Normal, Flying, Psychic and Dragon moves and are immune to Poison moves.
With 10 resistances and immunities against 3 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. 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 Ground moves. Avoid Grass, Ice, Bug and Steel moves, which deal little or no damage.
There is 1 Pokémon with this combination, such as Heatran.