If you're trying to level up and get all the items in your inventory, you're doing it the hard way: you're going through all the levels and beating all the bosses. But it's not fun, and it's not efficient. There's a better way: start with an empty inventory and get the items you need to level up by completing quests.

New Game Plus Plus is a tool that lets you start a new game with an empty inventory. All you need to do is install it, go to the main menu, and select a slot to place your items in. It will automatically place them in the right slot, and it'll keep them there. You can then go through the game and get the items you need to level up. It'll keep the items in the same slot, so you don't have to move them.