Okay, I managed to work out a solution to the above issue:
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×I placed one snake horizontally above the bottom door. I placed the other one so that it went from the northwest plate to the northwest arrow, which involved crossing the central plate. I managed to hit the orb in time and still clear out the roaches coming after me, then maneuver the remaining roaches in such a way that I could get four to the south side and get the orb between me and them.
Then I went northwest, killing one roach along the way, and managed to leave two roaches directly south of the snake and one roach on the row below that.
Now I have a new problem: the force arrow under the bomb on the east side.
This force arrow prevents the bomb from lighting the fuse until the pressure plate below the briar is activated. However, that plate is the only thing that opens the central door. And the big plate closes that door, but needs to be pressed down in order for the bomb explosion to reach the fuse.
I think I've hammered out the ridiculous process needed to resolve this, but I could use some advice on how to set things up for said process.
What I need to do:
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×-Get the roach and mimic on the east side near the briar
-Clear the big plate
-Get the roach onto the plate near the briar
-Walk onto the now-open door. In the process, lead a roach across the big plate, and hit the bomb with the mimic while the door is open
-Wait for the roach on the west side to reach me and kill it
The part that I'm most concerned about is getting a roach in position on the west side to cross the plate. Figuring out where the east roach and mimic should be is a bit of a headache, too.