Instructions
Defeat Yugi in a duel, including his Dark Magician. Before you even try matching slots this precondition must occur. Yugi is the final character boss if you fight under Kaiba's colors. If not, you must play through the entire game twice in order to fight Yugi.
Find an opponent you can defeat easily. You may select the wrong slot combination and even getting it right does not automatically produce Dark Magician Girl as a prize. Be prepared to duel multiple times before acquiring the card.
Select three Dark Magicians on the Graveyard Slot Machine. This combination does not always yield Dark Magician Girl, but if repeated enough times the card will be awarded.