That's a pretty tough room, there are several things that you need to keep in mind, here's some progressive hints:
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× While it's true that the final mirror's position is the eastern plate, you first need it to keep pushed down the southern big plate.
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× This way you can easily clear the tar, but not the tar mother yet...
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× Infact, after you cleared the tar, you need to push the mirror to its plate, which means that something else must press the plate, and there's only one thing left (unless you killed all of them).
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× The hardest part begin now, infact you'll need lots of babies to go back since the southern plate must always be pressed. Only when you take the second invisibility potion and step again on the door at (13,25) the plate is allowed to be released.
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There's not some other world out there where everything's gonna be okay.
There's just this one, just this rock.
-33th Skywatcher
