Pokémon trainers around the world are getting ready to return to Kanto (or visit it for the first time) in Pokémon: Let's Go, Pikachu and Pokémon: Let's Go, Eevee. Because they're targeted at a wider audience, the Let's Go games will be an easier and more casual experience (with a more "core" game coming in 2019), but there will be more challenging content for veteran fans after the main quest is completed.
In a recent interview, producer Junichi Masuda briefly commented on endgame content, including "Master Trainers." Masuda was later joined by artist Kensaku Nabana for an interview with Eurogamer, and the two elaborated further on these post-credit challengers.
Eurogamer: What would you say to those players who are crying out for a bit more of a challenge, maybe adult players who've been playing for these 20 years or who got into it a bit later? Should they wait for next year's RPG instead?
Junichi Masuda: So you know to those kinds of fans we'd mention the 'catch combo' mechanic, whereby you catch the same Pokémon multiple times in a row and get various rewards and benefits for that.
Kensaku Nabana: And also the postgame content as well, in particular the master trainers - so these are trainers who are kind of the ultimate trainers of a specific Pokémon, so you will challenge them. So you will challenge them, and then get their title for that Pokémon, so you become the master of that Pokémon if you manage to beat them in battle.
Junichi Masude: So for me, my favourite Pokémon is Psyduck, so I'd be training my Psyduck amazingly and then would challenge the Psyduck Master, and then gain the Psyduck Master title, and that's something you can put a lot of effort and a lot of time into, if I really wanted to create a challenge for myself - and these Master Trainers exist for all of the 151 Pokémon in the game, so you know, if you want to collect all of the titles then that's something you can really challenge yourself with.
It sounds like these Master Trainers will focus on a specific Pokémon, and you'll have to best them using the same Pokémon. It's an interesting way to get players to focus on monsters they might otherwise skip out on, but hopefully it's not the only type of extra challenge awaiting the League Champion. It'd be nice to see more variety in the post-credits challenges.