Garchomp is a powerful Pokémon with dual Dragon/Ground typing, which makes it weak to certain types of attacks. The following are some of the best counters to defeat Garchomp:

• Ice-type Pokémon: Garchomp is weak to Ice-type attacks, which deal four times the normal damage. Some of the best Ice-type counters include Shadow Mamoswine, Abomasnow, and Weavile.

• Dragon-type Pokémon: Dragon-type attacks also deal extra damage to Garchomp. Some of the best Dragon-type counters include Mega Rayquaza, Shadow Mewtwo, and Dragonite.

• Fairy-type Pokémon: Fairy-type attacks deal regular damage to Garchomp, but they are still effective counters. Some of the best Fairy-type counters include Mega Gardevoir and Togekiss.

Its important to note that Garchomp is resistant to Electric, Fire, Poison, and Rock-type attacks, so avoid using those wherever possible as they won’t do much damage at all. Additionally, Garchomp is immune to Electric-type attacks in the mainline games like Legends Arceus and Brilliant Diamond & Shining Pearl.

In summary, the best counters to Garchomp are Ice, Dragon, and Fairy-type Pokémon. Some of the best counters include Shadow Mamoswine, Mega Rayquaza, and Mega Gardevoir.