Well, for starters, remember about the Trick. How can it help you?
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× It doesn't seem to be doing much, but you cannot solve the room without it.
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× It does mean there is one obstacle in the "hostile" area, though.
So, your solution has to involve the Trick somehow. Do you see how you could use it?
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× Perhaps you could move the mimics around with it?
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× Looks like said mimics do not wish to help you out. What *else* can you use the mimics for?
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× What can be the use of the other orb?
And now a lot more straightforward (more or less direct spoilers):
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× The roach has to kill the serpent, not the mimics.
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× The mimics are used to direct the roach to the serpent.