Obviously you're on the right lines as regards what you need to achieve...
If you can't see how to get to the orb from the roach then:
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×Everything might not be as solid as it seems.
If you're having problems manovering the mimic:
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×Use the walls and pits to your advantage.
Also, is it necessarily clear which mimic should be used with each section of the room?
(NB: This last point may be either a hint or a red herring, I haven't played through the room recently. But it's certainly a valid point.)