Time Piece exploit
I looked around and couldn't seem to find anyone discussing this, so here goes:
Did you know that you can sell items you buy via Hermes' Shrine and gain <×2 the amount you spent? Buy an item twice (for express) then sell it for profit. These appear inbetween Surface regions and so if you check the shop and see there are 2-3 things you do not care for, but you got enough gold to buy them, pick Time Piece for some easy cash.
Makes this item go from "nice to have" to "will give free gold". As long as you didn't spend it all before the previous boss.