I am having a hard time beating Junker in Peach's Castle. Mario and Luigi are at Level 18. Do I need to level them up more before fighting Junker? I am basically getting OHKO'd my Junker. Will leveling help or do I just need to practice more?
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Even though I only fought him a few days ago I don't remember my level, but I would imagine 18 is on the low side. You're actually coming into the final stretch, and I was 33 at the very end so it would probably help greatly to level them up a bit. At 25 IIRC you get access to the final store which has the best armor at 20k coins a pair, so you might want to start saving up now if you don't think you'll have enough. He is a tough boss though, I remember having trouble as well.