There are a few bugs to utilize first off
1. You can infinitely dupe statues of perfection by placing them down, mining them (but not picking them up), then going to the shrine and getting another
2. I believe certain multiplayer dupes like table duping exist, basically two players spamming an item on a table and it just gets slowly duped
There are also certain things that have been removed in 1.6 that could be considered exploits, namely making cash with basically no in game down time with the casino. Not exactly incredibly overpowered unless you want to stick around and grind out qi coins for marginal profits (relative to the crazy low buy speed of switch), but it's still an option