Modding refers to the process of altering a game's code or data to change its behavior or unlock previously inaccessible features. In the case of Yu-Gi-Oh! Duel Generation, players want to unlock all cards to gain a competitive advantage, experience the game with a complete set of cards, or simply to satisfy their curiosity.
If you have applied a mod and the cards are still missing, try these troubleshooting steps: Filter Checks yugioh duel generation mod unlock all cards fix