Duplicate Items
You can duplicate any item by a very easy method. Simply find the item you want, then save. Pick the item up from the ground or your inventory so it replaces your cursor, but do not drop it or put it in your inventory, Reload your save file. The item should still be where you picked it up from AND on your cursor. You can do this to duplicate rare, powerful items like Mind Crystals, Knowledge Brew, and one of a kind weapons. Try selling duplicate Demon Slayers to make ridiculous amounts of gold lightning quick.