There are basically two steps to setting this up, aside from opening as many doors as you can before crossing:
Click here to view the secret text
×-Get a goblin to (10,30)
-Get a wraithwing to (35,16)
Once you've managed that:
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×Lure the second goblin to (36,5). Now the other goblin will walk right to the plate which closes the arrows, and you'll have time to kill the goblin near you before it does.
It should be pretty simple to clean up from there, provided you don't foolishly summon the soldier first like I did. That's still possible, but a lot harder.
