Mami discovers a level 58 Mightyena! Fetch is its absolute favorite game in the world. If Mami puts something down, it thinks she wants it to retrieve that item. If Mami throws something, it thinks that's a cue to chase it. The same applies to any object handled by her Pokémon, too. And when there is nothing to fetch? It will pick things up at random and trot over to Mami to ask her to play.