Sounds like you are able to get the clone potion. You should place the clone
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×on the checkpoint below the goblin and the roach.
Next, you can kill that lower goblin and roach, as well as the upper left roach near the decoy potion. You'll need to do a lot of switching back and forth between Beethro and his clone - TAB key or click on one with your mouse. Just when a monster is about to get Beethro, switch to the clone, and the monster will step away towards the clone.
Use the decoy potion to
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×kill the upper right roach near the invisibility potion.