Mimic allows your Pokémon to copy an attack from its current enemy.
When Mimic is used against a wild Pokémon or a game trainer, you are
presented with a menu from which you may select the attack of your choice.
When Mimic is used in a link battle, it copies a randomly determined
attack.
Once your Pokémon has copied an attack, it will retain that move until
it is switched away for another Pokémon. Mimic takes the max PP value from
the enemy, but its current PP remains normal. Suppose a
Dodrio steals
Surf from a
Starmie. Dodrio originally had 10 of
10 Mimic PP. After Mimicking Surf, it now shows 9/15 PP. That's 10 minus
1, for the one use of Mimic and the 15 comes from Starmie's max PP for
Surf. If the Dodrio uses Surf on the Starmie, it'll then show 8/15 PP:
9 minus 1 for another use of Mimic.
Despite being a Normal type attack, it is effective against
Ghost Pokémon.