Ashlesha is the tamasic aspect of Mercury. The energy of Tamas strips away, destroys.
Ashlesha is the energy of Mercury which uses the intellect, our discriminative capacity, to strip away false identifications. This is Self Inquiry.
Since Ashlesha occurs in the final degrees of Cancer, the Moon (our right-brain, intuitive, emotional nature) is still in its own house. So we have the penetrating insight of Mercury as the watchful intellect which penetrates deeply beyond the emotions and witnesses each thought as it arises and knows it is not that thought, that emotion, nor anything in this changing field of life. We are Empty Presence.