@xXSaadXx0 I make a deck on any emulator like Dueling Nexus or EDOPro and find out how I want the duel to go. Sometimes I’ll use a deck shuffler or randomizer to get ideas. Other times, especially for important moments, I choose specific cards deliberately to highlight a character’s strategy.
I don't know how other authors handle it, but I aim to minimize errors as much as possible so the duels feel believable. In the past, I’ve read Yu-Gi-Oh fanfics where certain plays or turns didn’t make sense or didn’t follow the game’s mechanics, which pulled me out of the story. By approaching it this way, I can be far more confident that the duels are accurate and consistent.