I wanted to create a Pokemon challenge so, here we gooo!

1. Starter Only!
You can only use your starter for battles. (you can also use others Pokemon ONLY for HMs.)

2. Healing Restriction!
You can heal only one time at a Pokemon Center before a Gym. (Let's imagine: you arrive to the 1st gym, you can heal, but after clearing that gym, you can't heal anymore until you reached the 2nd gym.)

3. Saving Restriction!
Just like Rule 2., you can save only before a gym...(...yeah, maybe I'mma erase that-)

4. Full Offensive!
You can't use attacks who doesn't damages. (like Status Attacks: Toxik, Spikes, Rain Dance, Dragon Dance, etc...)

5. No transformations!
If you wanna do that challenge in Gen 6/7/8/9, Mega Evolution, Terastal and Dynamax are a no-no.

6. STAB Only!
You can only use attacks who match the starter's type. (so, Sceptile could only use Grass attacks, Infernape could only use Fire and Fighting attacks and so on...)

7. No Healing/Battles Items. No Flee.
The title says all...

8. Leveling stucked to Gym Badges' "traded Pokemon still listening orders".
...I'm not really sure how to explain that, I think that's self-explanatory.

9. No Point in Dying
No K.O allowed in the whole gameplay or you return straight to the start-

10. No E(e)V(ee) Training.
Self-explanatory.

Bonus 11.: "Even Harder!"
Maybe try that challenge in a Pokemon Romhack?

Bonus 12.: "Evolution is the Weaaks"
No Evolution. (isn't that just an impossible challenge with that-)