Here's something similar to noma's that worked for me. This should get you enough time. Basically for this room you want to make as circuitous a rout as possible. Making the roach do a basic "
Z"
shape seems a good way to do it. Structuring the rock piles to make the roach go to the bottom right corner, then to the bottom left, then to the top right should get the job done.
What's that? Oh yeah, I guess Challenge: Don't use the potion.
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