Garchomp is one of the most powerful non-legendary Pokémon you will encounter in Pokémon Brilliant Diamond and Shining Pearl. When you reach the final battle against Cynthia to decide the Pokémon champion, this will be one of the toughest foes to get past. Here are some moves and Pokémon you should use against Garchomp.
What is Garchomp weak against?
Garchomp is a dragon and ground-type Pokémon that evolves from Gabite and Gible. To take advantage of it, you will want to use ice moves first if you have them. They are the most powerful against dragon types, so if you have Ice Beam or Blizzard, rely on them. If you do not have either of those, focus on fairy or dragon moves against it. Moon Blast, Roar of Time, Outrage, or Dragon Hammer are our recommended moves.
As for moves to avoid, Garchomp will not take any damage from electric moves and is strong against fire, rock, and poison moves.
As stated above, ice moves are the most powerful against Garchomp, but there are not many choices from that category. Abomasnow is probably your best choice from that list of Pokémon with Mamoswine and Weaville taking up the back. Otherwise, you will want to rely on teaching Ice Beam or Blizzard to any other Pokémon that can learn it.
Outside of ice-type moves, Palkia or Dialga can be strong against Garchomp and survive its attacks better than some others. Other strong choices include Gardevoir, Togekiss, Gengar, and Mew.
As for Pokémon to avoid when fighting a Garchomp, particularly you want to avoid anything with low defense. Unless they can outspeed Garchomp, it will take them down in one hit with its powerful attacks. Avoid fire, rock, and electric type Pokémon at all costs.