×1) The east mimic potion must be taken first and results in a mimic at 34,15 facing NW.
2) Once this mimic is placed, no sword turning is allowed until the room is cleared and Beethro is by the exit.
3) The only thing that can be done at this point is to take the 2nd mimic potion.
4) That mimic must be placed at 21,28 facing NW.
5) That mimic must not be allowed to move for a turn. To accomplish this, Beethro may go S, E, or wait. Otherwise the roach is trapped.
6) Now the goblin is directly next to Beethro and there is no way to escape it. The crumbly walls and pit seem useless.

×5 of these assumptions are correct, 1 of them is only partially correct. Specifically:

×Thanks. Looks like the crumbly walls are useful after all. Keeping the roach east of you so you can get into a position to kill it was the hardest part.