Sadly my starter was Treecko, and my Lunatone cant kill Ninjask, just 1 or 2 hits can defeat my Lunatone, but he is faster and I need like 4 hits to defeat the Ninjask... I dont know what to do anymore..
Unfortunately, it’s been a long time since I last played, so I couldn’t tell you the exact strategy, but I’d say a Beedrill with Fell Stinger, Poison Tail, or First Impression could help you. I think you can get them in the first few towns.