The soldier is trying to kill the spiders, he's just bad at going round corners.
The key to dealing with this is a mechanic that wasn't really dwelt on in the main game. When you use a soldier horn, the soldier enters
facing the same way as you. Also, despite the symmetry of the room, he targets the eastern spider first.
This means you should
Click here to view the secret text
×take the horn facing SE, so the soldier can go straight for that spider without needing to turn.
Both slimm tom's and bwross's positions for the mirrors are valid solutions.
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50th Skywatcher