To all the people who say that the episode could've done without the time-travel, here is why I think it was necessary:
1) 10 years is a long time, Yolton would've become broken and dispirited over the duration of that time from losing his hotel to a bunch of crooks. He would've lost his reputation, his relationship with his family (wife and children if he had any) would've become strained, trust would be lost from the townspeople etc. etc.
2) The Pokemon that the Mantle took from all the trainers over the years would amounted to the 100s if not 1000s. This would take a long time to track down all those people to return their Pokemon to, they could be living all over the world in Kanto, Sinnoh etc or be deceased. Even if they did manage to track them all down, the relationship and trust that the Pokemon had in their trainers would've been tarnished and difficult to repair.
3) Yolton entered into a verbal agreement with Mantle to hand over his hotel if he lost, so calling Officer Jenny wouldn't have been much help. Sure, he was practically forced into the battle, but Yolton may have been too proud or weak-willed to risk getting the authorities involved. The crooks could've come after him (or his family) and hurt him/them.
If these events had taken place over the course of a few days/weeks, then the time-travel wouldn't have been necessary, but this is 10 years we are talking about. It's a long time.
