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Luz entered the house and got transported to the Boiling isles, not aware of the two cat-like eyes that had watched her the whole time. From the treetops, a shadowed figure hung, its eyes glowed as it cackled. It sounded amused and crazed at the same time. The figure let go of its perch and fell down. On the grass landed a perfect copy of Luz. It strode back to the street, giddy and bouncing as it waited for the bus. There was a lot of potential chaos it could do. After all, freaking out humans was its favorite hobby.
So, basically there was a doppelganger nearby that saw the whole thing and decided to turn into Luz and cause chaos in the camp.