One of them is, yeah! This is Goodra's ball - the big purple dragon you saw.

[ he takes the opportunity to pull out the rest - indeed, there are as many as the number if Pokémon that Aerith saw in his memory. Duraludon looks over curiously, possibly hoping that his teammates will somehow crack out of their temporary holds... ]

We Trainers use Poké Balls to keep our teams portable. I dunno how it works exactly, but they basically change a Pokémon's form into data and keep them in a comfortable stasis. They're safe and healthy where they are, but I want them to see this place for themselves...