In battle, the user sets off an earthquake that strikes every Pokémon around it. Smashes a tail, foot, or fist into the ground, causing an earthquake. It inflicts double damage on a Pokémon that is underground (i.e. using Dig).
You can make a double battle combo with 1 of your partner's Pokémon if they're a type weak to Ground moves. Let them use Protect, Magnet Rise, or anything protecting them from ground moves and then use Earthquake. It should hit the opponents Pokémon hard, and your partner will stay protected.