Monster Falls

Mabel, Dipper, and Wendy find a strange river- it's the clearest river they've ever seen, and it tastes sweet, almost addicting. When they swim too long and Stan has to come find them, finding the river in turn, he decides to bottle the water and sell it. What they don't know, is that Stan's sold water to the whole town from the Deum Flumen Cantata, Fluvius Cantata for short, and even Ford doesn't have the cure for it.

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I just have to say, I think how they get back to being humans is the best solution of all the Monster Falls, I'm just saying. Prepare for laughs and easter eggs!