In the Union Room, you can Mix records with up to 5 other people in Generation IV. This mostly affected television shows and dressed up Pokemon in the Fitting Room of Jubilife TV.
Interesting fact: This also affects the Great Marsh! While this is much less convenient due to Marsh Pokemon being randomly selected, it could potentially make hunting for a rare encounter Pokemon such as Azurill, Carnivine, or the Post National Dex encounters a lot easier if you have multiple games hunting for one,