Grandpa Muto

How to Unlock: When you are at the Title Screen, press L, Right + B, Right, B,
R, Left, Down, and A.
Super Power: Rule Change - Can randomly increase or decrease the number of
stars needed to win.


Kaibaman

How to Unlock: When you are at the Title Screen, press Down, B, Left, Right,
Right, R, Up + R, and A.
Super Power: Lose Turn - Can make his opponents lose their next turn.


Yami Bakura

How to Unlock: When you are at the Title Screen, press the L, Down, Right, Left
+ B, R, Down, Down, and A.
Super Power: Absorption - Can absorb 1/8 of each of his opponents' Life Points.


Yami Yugi

How to Unlock: When you are at the Title Screen, press R, Left, B, Right, Up +
R, Right, Down, and A.
Super Power: Higher Chance - Can give him a higher chance of rolling a Star
Face.

Pick Yami Yugi set board stars to 1 or 2 so the game ends quickly 1 may require a few rewinds if the opponents go first and get good rolls. If someone else rolls before you and gets a space just rewind. You want to load your dice with 4 star monsters and lower so you can actually use them to battle. Yami Yugi Super Power gives a higher chance to get your preferred card aka star face. Stars are earned by taking spaces on the board so with this method you should be able to get the achievement in a few minutes