Unfortunately, I have lost all my demos for this hold, but I can tell you that the solution does not have to be trial and error. I presume you're having trouble with trapping two slayers at once. Scheming, plotting, and diligent counting of squares can get those two slayers locked up for you.
How to do it:
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×1. Run around the room until you have large separations between Beethro, the first slayer, and the second slayer. Their wisps should be exactly overlapping.
2. Count squares along the wisp between the two slayers.
3. Lead the slayers on a path between the two traps. This path should have exactly the right number of steps (counted in step 2). The path should stay 5 or more squares away from the orb you will have to hit.
4. Stand by the orb and wait
Also, remember that stepping into a 4x4 square with a slayer will stop him from following his wisp. Make sure you don't accidentally stop a slayer when he needs to keep moving in step with the other slayer.