>>38402409>You would actually need to find a way to grind it to level 5 (supersonic) without using tackle/ember/whateverCatch one at level 4, then catch wild Pokemon without attacking them (which still gives you XP) to hit level 5. The only problem would be if there are any trainers you need to beat to get to Dark Cave. I'm not sure, but if there are then your best bet would probably be to pick Cyndaquil, get it to level 6 via the same method, then PP stall your opponents with Smokescreen/the Stringshots of any Caterpie/Weedle you've caught.
Like I said, the challenge doesn't really seem difficult in the sense that e.g. a nuzlocke is difficult, just incredibly tedious and time consuming.