I had this challenge in my head, and I'm currently testing it. I'm okay if people add some extra suggestions for this or if there's any reasons why this challenge is a bad one. The main goal is to encourage players to use Pokemon from later routes and not sticking to the ones you had early in the game:
The Tinkerman Challenge
1. For each route/area, you
must only pick one Pokemon (preferably one which you haven't used it before), and put it on your team. Your starter counts as an area. You can catch as many Pokemon as you like for every route, as long as you pick only one Pokemon per route on your team.
The Pokemon must be different. I'll pick Pokemon Red as an example:
It's basically kinda like a Nuzlocke, but the difference is you must put one from each route in your team. No "catch the first Pokemon you see" rule, just you can pick only one Pokemon from any Pokemon in each route.
2. If it has reached a point where the next route has all the Pokemon you already have, you can skip the route.
3. If the route has only one Pokemon (I'm looking at you, Unowns from the Ruins of Alph), you can either have the choice to put it on your team, or skip it.
4. For gifted Pokemon, you can have the choice to either put it on your team, or skip it as well.
5. If you reached a point where you run out of money for Pokeballs, you must sell some of your items to get some money to buy them. If you're really broke, you can battle trainers from later routes, but you
still must put one Pokemon per route in your team.
6. Once your team has 6 Pokemon, for the next route, you
must replace 1 of your 6 main Pokemon with a new one from the next route. Yes, this means that your final team will include one Pokemon from Victory Road.
7. Of course, you would think,
"Oh, that's easy, I can just have the 6th Pokemon be Pokemon from the new routes and I'll just replace it often every time I walk into a new route".
Nope, once you got at least 6 Pokemon, for every new Pokemon per route, they have a
"4 Routes" limit. This means that these new Pokemon
cannot be replaced until you passed 4 routes. Yes, this means that you could keep your starter (or your other preferred Pokemon early in the game) and/or your HM slave until the end of the game, with the other 4 being the Pokemon from the new routes.
8. And once you replace your old Pokemon with your new Pokemon,
you cannot use your old Pokemon anymore. You
may use it for grinding purposes, but you cannot use it to battle trainers/gym leaders/Elite 4/Champion.
9. Your final team's levels must be at least the lowest level of the first member of the Elite 4.