As you level up, points get harder to earn. If you want a fast way to increase your character's stats and level, you should have a fairly powerful (L13+) Hyakki Yako weapon (high stance) and the Cowboy Accessories Set (or any accessories that give you a large amount of MP). Enter Stage 14 Wilderness on Normal or Hard difficulty and turn on the Custom Rules for Constant Master Mode, No Falling, No Grabbing, and Under Time. Go through that stage and kill all the enemies as usual. At the end, you should jump up quite a few levels. If Gojiro is already at Level 99, playing through Stage 14 with those four custom rules active will pretty much top off an entire level each play. (Note: you will not be able to increase the performance of accessories or weapons due to Master Mode being constantly on).