A strange thing happened on the way to the Ruins

[evereve]

Wearing my new goggles to combat the harsh sandstorms of Hoenn's desert, Route 112, I challenged a Camper on the North side to a battle. He sent out his Sandshrew and used Dig. I had my Nuzleaf, daatengu, use Nature Power which turned into Earthquake. Their Sandshrew fainted while underground ... how does that work‽ It makes logical sense; normally most attacks don't hit underground. But how did Sandshrew return to it's monster ball?