It is completely clear that Srila Bhaktisiddhanta defines tatastha sakti differently than all of the above posts suggest:

"Before acquiring material designations, the living entity is supremely
pure. Even though he is not engaged in serving the Supreme Lord, he remains situated in the neutral position of santa-rasa due to his marginal nature. Though the living entity born from the marginal potency does not at that time exhibit a taste for serving the Lord due to a lack of knowledge of self realization, his direct propensity of serving the Supreme Lord nevertheless remains within him in a dormant state. Though the indirect propensity for
material enjoyment, which is contrary to the service of the Lord, is not
found in him at that time, indifference to the service of Hari and the seed
of material enjoyment, which follows that state of indifference, are
nevertheless present within him.

The living entity, who belongs to the marginal potency, cannot remain
indifferent forever by subduing both devotional and nondevotional
propensities. He therefore contemplates unconstitutional activities from
his marginal position. As a sleeping person dreams that he is active in the
physical world without actually being involved in activities, when the
dormant indifferent living entity of the marginal potency exhibits even a
little apathy to the service of the Supreme Lord and situates himself in a
neutral, unchanging condition for even a little time, he is infected by
impersonalism. That is why the conditioned soul desires to merge in the
impersonal Brahman, thus exhibiting his mind's fickle nature. But due to
neglecting the eternal service of the Lord and thereby developing the
quality of aversion to the Lord, he cannot remain fixed in that position. In
this way aversion to the Lord breaks his concentration of mind and
establishes him as the master of this world of enjoyment.

(Srila Bhaktisiddhanta Sarasvati Thakura: Brahmana and Vaishnava,
Hari-jana-khanda, p. 86-87)


Jivas are of two kinds (1) Nitya-mukta (eternally free), (2). Nitya-baddha
(eternally enslaved). Free jivas are never enslaved. They are serving the
Supreme God in five different functions in His eternal blissful abode, where
there is no change, no destruction, no misery. Jiva, once entered there,
never comes back here.

(Srila Bhaktisiddhanta Sarasvati Thakura: Vaisnavism - Real and Apparent,
"The Bondage of the Jiva")


Vishnu has three energies, one of them is meant for manifestation of His
eternal Abode, another Potency is for creating all human souls who are
emanations from His Tatastha-shakti found between the temporal and eternal
worlds. By this potency He creates human souls. The human soul has two
different predilections. If he desires to serve God-head he is allowed into
the Eternal Region. If he desires to lord it over this world he comes down
for enjoying in different capacities the products of the Deluding Potency.

(Srila Bhaktisiddhanta Sarasvati Thakura: Sri Caitanya's Teachings,
"Immanent and Transcendent")