What does the manas grasp as "self" in its self-grasping?

The manas's grasping at self is innate, and is called innate self-grasping (sahaja-ātma-grāha). It mainly grasps the five aggregates and eighteen realms as self and as belonging to self, as having real function—grasping at self, at a person, at sentient beings, at a life span; grasping at the six sense objects, at the functions of the six faculties, at the knowing and seeing of the six consciousnesses, at feeling, perception, formations, and consciousness, and at the physical body. As for the grasping at other, subtler dharmas, it is named dharma-grasping—grasping dharmas as real, as belonging to self, as having actual function. Of course, when one does not yet know or understand many dharmas, there is no way to grasp at them. As the degree of one's cultivation deepens continuously, and one comes to know more and more dharmas, ever subtler ones, the mind's dharma-grasping will keep appearing and growing stronger, and one must continually engage in contemplative practice (vipaśyanā-caryā) to subdue, remove, and sever it.

The mind consciousness also has grasping, only not as severe as the manas's; it is a grasping at sense objects that arises only when one is in the midst of those objects. The more one contacts the six sense objects, the more and heavier the grasping becomes; this is called discriminated self-grasping (parikalpita-ātma-grāha). The mind consciousness's discriminated self-grasping is intermittent, present at times and absent at others; when the mind consciousness ceases, the grasping ceases; when the mind consciousness understands principle, the grasping is subdued or perishes. The mind consciousness's grasping at sense objects is lighter than the manas's grasping, not so obstinate—it can be relinquished the moment one resolves to let go, and perhaps after a night's sleep it is forgotten. The manas's grasping, however, cannot be forgotten even after a lifetime of sleep, cannot be eliminated, is obstinate to the extreme; and at times, the more it is opposed, the more obstinate it becomes.