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first place the clone (sword south east), then kill the adder. Sword position must not change.
then wait a couple of turns and move into the hallway eastwards, until the southern roach gets killed on the hotplate.

start the timeclone and watch, while recorded beethro kills the adder.
while he waits, move into the big chamber and stand next to the roach.
when recorded beethro steps onto the pressure plate, you have one turn to kill the roach, before you loose your sword.
but its enough.