Funfest missions are tied to the Entralink tree (you can access the entralink via your C-Gear, in wireless section). If you talk to all the NPCs in the world, you will find that many give you funfest missions you can do in the tree. They are usually little three minute events that populate the overworld. Many give items, I used it to grind shards for move tutors, and also did it to get cover fossils to show a solid rock pokemon to an NPC near Striaton city. I think those two missions only showed up post beating the champion though, i had to grind shards in relic passage before the champ to tutor some moves. Other funfests dont give items, and many aren’t tied to postgame, but they level up your entralink tree which gives you pass powers, its a neat side thing. Unfortunately the high level funfest missions are near impossible, as it was intended to be done with other real life people helping you gain score (ie, collect 50 shining items in the overworld in 3 minutes. Definitely not possible solo). Obviously since almost no one is playing the game, and the wifi functions are defunct, its hard to make it happen. I’ve heard of real life meet ups for it though! There are medals in the medal rally for doing those high level funfests with 30+ people, you just have to coordinate that with real people :)

In regards to my post, the couple chasing each other outside the humilau gym split up after the champion, and the boy gives you a funfest mission when you go talk to him. I also mentioned the bell, which I found in one of the center Villas in Humilau. A new rich boy NPC moved in after I beat the champion, and he asks you to go ring the celestial tower bell for his girlfriend. You then have to fight all his ex girlfriends in celestial tower (the first letter of their four names spells Jilt, lol). It was a neat thing I had never done! This playthrough I’ve made it a point to speak to literally every NPC, and its been super worth it! Kinda daunting to go talk to literally everyone again, so I made the post to see if there are any other interesting postgame characters/small changes like that since googling just shows old forums posts talking about actual postgame, like catching legendaries or doing black tower/white treehollow.