There's a secret boss at the very beginning of Chapter 5 that I highly recommend fighting.
Spoilers!
At the very beginning of Chapter 5 (THIS IS YOUR ONLY OPPORTUNITY TO DO THIS) backtrack aaaaalll the way to Osohe castle and climb back up to where you fought Mr. Passion. You'll fight an updated version of him that rewards you with a pair of Fantasy Shoes for Duster that add +40 attack as well as some other sweet bonuses.
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