The user burrows, then attacks on the next turn. It can also be used to exit dungeons.
Dig can target any Pokémon adjacent to the user. Dig has the user burrow underground on the turn it is selected on, avoiding all attacks except Earthquake, Fissure and Magnitude. If Earthquake, Fissure or Magnitude are used on the user while it is underground, the damage to the user will be doubled from what it would have done if the user was surfaced. On the next turn, the user resurfaces and attacks the target.
Outside of Battle
In Generation I, when used in caves, it transports the player to the last Pokémon Center they stopped off at. In Generation II and onwards, when used in caves, it transports the player to where they entered the cave.