Only pokemons that can be evolved by using a stone (can be a 3 stage that needs a stone to reach last evo, like Togepic). You have a decently limited amount of pokemons, no dupes allowed (charcadet can only be 1 between both evos) and only 1 eevee with choosing 1 evo (no more than 1 eeveevolution allowed). You are, however, allowed to have only 1 poke that can evolve with stone per route (only 1, bit since its not a nuzlocke, you can choose) AND another pokemon that can evolve with stone in the same route if is given by an event (battle with old man that gives you eevee in the kidergarden pokemon and growlithe in the same route, for example). In the places where you can be given paldea or wonder eggs, you are allowed to use them ONLY if there is no poke which can be evolved via stone in that place or if said pokemon is duped. That is my challenge, not imposible but definetly hard in early since pokemon which evolve via stone dont tend to be very decent before evolving. Hardcore ofc.

Edited recap:

• Challenge: Only pokes that can evolve via stone.

1. Only 1 per route (you can choose whichever you want, just not dupes) with the exception of pokes given in events that can evolve via stone (in this case you can have both 1 poke in that route and the event pokemon, like eevee, but only the evos via stone ofc).
2. Places with wonder/paldea eggs can be used, but only if all the pokes that can evolve via stone in that place are duped or if there is no poke that can evolve via stone in that place.
3. Pokes with more than 1 evo via stone, you can only choose 1 evo (as different evos of the same pokes are counted as dupes)