I guess it's a Summer camp gag. How so? Team Rocket have been working as disguided staff in the summer camp, and they may want to steal Pokémon, but since they are getting well paid, I think that, to keep being there and trying to steal them, they will keep their jobs, but a different job everyday, maybe on next episode they will be rock climbers' assistants/helpers/guides.
Now, I will picture/predict how the cliff scene will go.
Serena runs off to search a place to film, followed by Ash, leaving the group behind. She gets there and Ash eventually catches up, so Serena looks around, imagining how her Pokévision will go, and suddenly, a piece of ground below her crumbles, breaks and falls. She falls with it, and Ash takes her hand to try to save her, but she eventually drags him down with her. TR, who are climbing that cliff, go and save them, since they need the money and need to do their job correctly. Judging by the preview, there is no Pikachu with Ash, so they can't steal it (plus if they reveal their identities, the whole gag for all the arc would come down, since they would obviously be sent blasting off by Ash and Serena away from the camp and wouldn't be able to return and "work" normally). Once they are on safe ground again, they thank the TRio (without knowing who they really are) who dissapears from there. Then Ash and Serena have a little talk. Like Serena thanking him for trying to save her, but also apologizing since it was her fault he had to save her and come down with her. Ash telling her to be more careful when looking around like that, and (upcoming part is what everyone has said and I guess also expect) Serena asking him why did he risk his life to save her, and goddamit Ash you better answer something good, cause I swear if you say something oblivious like: "HEY WE'RE FRIENDS, RIGHT? I'D DO ANYTHING TO SAVE MY FRIENDS!" with the biggest dense grin on your face and a happy/upbeat tone on your voice, and make Serena feel bad and/or friendzoned, I don't know how but I will go and kick your *** back to the bottom of that pit.
Edit: YAY 800 PAGES!!!