For this to work you need a Failure title, which can be acquired randomly from the type of creatures Marona can summon. You'll also need a dungeon. The dungeon you'll want will need a level much higher than your character's, but set with few enemies and preferably with lots of items.
It's exp gravy train from here. This video shows that it takes a little bit to get the whole thing set up, but once it's up, it works and it works well.
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