Yu-Gi-Oh! Ultimate Masters: World Championship Tournament 2006

This might be my favourite battle simulator from the Yu-gi-oh franchise, although considering the lacklustre competition that's hardly saying much given how it does this by doing the bare minimum of having an intense progressive system.

By all accounts this is a basic game, you duel the different monsters the game had to offer (this being the main gimmick of gx which introduced the concept of duel monster spirits in the franchise) with their being three different styles of duelling you can choose from. There's free duelling where you battle against monsters with themed desks without any restrictions or gimmicks, there's limited duels where you have to duel these monsters with restrictions such as not using certain cards or mechanics in a duel, and then there's theme duels where you must win a duel after fulfilling a certain condition such as using x number of certain types of cards. There's also the return of duel puzzles, something the franchise quickly becoming ubiquitous for following their introduction in nightmare troubadour (and thankfully aren't as cheap here as they were there.) Something that's a first to this game is that booster packs are the same as the real-life tcg packs as well as other themed packs to accommodate for ocg exclusive cards, although this isn't a complete database for the time as several 5- and 6-star vanilla monsters are absent from the game likely due to how useless they were at the time in the meta. The game also lets you choose one of the five original structure desks from back in the day as your starter deck, although they weren't very good even at the time so it’s not like you had an amazing deck right out of the gate.

It's a great battle simulator and a major step up from most duel monsters era games, a bit generic sure, but a good gateway into getting into the early gx era of the franchise.