There are seven Riddler Trophies in Cauldron South. I recommend saving Riddler Puzzles until you've completed the main story, that way you've [unlocked all characters](https://www.eurogamer.net/how-unlock-all-playable-characters-lego-batman-legacy-of-the-dark-knight) - some of whom you'll need. On that note, here are all the Lego Batman: The Legacy of the Dark Knight The Cauldron South Riddler puzzle solutions.
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