Title Screen
Successfully beating the game changes the opening title screen from blue to purple. However, inserting a special code allows you to switch the title screen color back to blue. Simply press "Up," "Down," "Down," "Left," "Right," "Left," "Right," "B," "A" while on the title screen. Using the same code also changes the screen from blue back to purple.
Dragons
To enter card cheat codes, press the GameBoy Advance's "R" button at the password machine and then type in the numerical code. You can use several codes to get dragon cards. The code "86164529" earns the Aqua Dragon card. Type in "81480460" to acquire the Barrel Dragon card. Enter "11901678" to get the Black Skull Dragon, which attacks with molten fireballs.
Weapons
You can use some cheat codes to acquire weapon cards which can then be paired with monsters to upgrade their attack points. For instance, the code "18937875" unlocks the Burning Spear card that can upgrade the attacks of a fire monster. The code "22855882" earns the Fiend Sword. Enter the code "61854111" to unlock the Legendary Sword, which increases the attack and defense for monster-type warriors.
Beast Warriors
Entering certain codes unlock beast warriors, imposing fighters who are half human, half animal. Typing the code "21340051" earns the Boar Soldier card. Use the code "42035044" to get the Panther Warrior. To earn the Alligator's Sword card, type the code "64428736." And the cheat code "49791927" unlocks the Tiger Axe card.
Clowns
In Yu-Gi-Oh, clowns are no laughing matter. These fiendish warriors and spellcasters possess great power and vanquish enemies while wearing evil grins. Entering the code "17511156" earns the Wood Clown card. Typing the code "13215230" gets the Dream Clown card. To get the Mystic Clown card, type the code "47060154." The code "66602787" unlocks Saggi the Dark Clown, an unpredictable magician. And the code "42647539" acquires Ryu-Kishin Clown, a demonic fiend.