I really get annoyed when I get sleep vials, and wonder to myself, "Will there be sleep monsters, or is this the most non-helpful item?"
I mean, it is helpful for stopping your enemies for awhile for the cost of their health going back up, which i dont really find great.
Vials and Plate line weaknesses are all we have in reference to sleep. Slooms were removed.
Since this is your suggestion you are supposed to suggest a new use for it. Herp derp.