We can start another thread to discuss the transcendent function if you like.
I haven't read Psychological Types in a long time (as you know, it's not one of my favorites), so I don't recall the details of Jung's arguments. For instance I'm confused about the descending/ascending idea you bring up in regards to the transcendent function. Is that the way Jung contextualized it or is this something you are adding?
I do remember the notion of the transcendent function in terms of a third position that, in essence, is the gravity that pulls the Opposites together toward union. It is a kind of new sun and the beginning a new solar system. Initially, it is an abstract and symbolic goal . . . very much like the alchemical lapis philosophorum (or one of its manifestations like the White or Red Tincture, the Gold, the Quintessence, the infans solaris, the Resurrection, etc.).
I don't recall Jung's exact formulation (I just remember feeling that Jung's notion of the transcendent function was a little hazy for my taste), but I can say that, based on my own personal experience, I think this imagined goal ends up being something completely different by the time the individual arrives at its doorstep. When we start out, we don't understand how to value this "transcendent function". Therefore, a numinous valuation emerges out of the unconscious. It tells us that there is great worth in this mysterious new goal. It tells us how it feels, how we long for it . . . but it doesn't tell us what the thing is. So this emergent symbol is often very vague . . . perhaps something like a mandala or generic Self symbol, something geometric and abstract. It is an "Everything/Anything symbol", in a sense.
The trick (for the individuant) is to not get sucked into literalizing it or totemizing it . . . i.e., making it into some distant constelation off in the heavens that can only be worshiped and gawked at, but never interacted with. This is the egoic impulse, and it usually accompanies an inflation of sorts. In that inflation, one either becomes a priestly devotee (and protector/defender/prophet) of this symbol or else identifies with it directly, trying to don its numen like a coat of many colors.
But, to arrive at the coniunctio* is to recognize that this third position is one at which one is able to value the first and second positions equally and make differentiations that determine when one position is more appropriately applied than another. This is, I think, experienced as an enantiodromia, even though it is actually a movement toward a "third position". But the third position feels like an Opposite of the initial position . . . and in a sense it is, because it is a conscious valuation of the true opposing position (which by necessity involves a depotentiation of the primary position). Jung didn't always define enantiodromia in this (more positive) sense . . . but I'm personally inclined to use the term for this "transcendence" to the third position (probably because I don't like the term "transcendence", as it is too abstract and too prone to inflated egoic notions . . . and because nothing is actually transcended in this coniunctio; it is merely an addition of valuation). The more negative (regressive) kind of "enantiodromia" is maybe better described with Freud's term: reaction formation.
* (This is something a bit different than the animi coniunctio, which may be seen as, in some ways, the first "transcendent function" in which the third position becomes the primary position that defines the "new ego". I think this has less to do with types of cognition and more to do with becoming a conscious individual, though.)
So, arriving at the goal of the third position "in the flesh", one tends to find that the "stone is worthless". That is, it possesses no value as a currency, grants the ego no greater power. The stone is the value of valuation itself. The preliminary imagination of the goal tends to bring up dreams of "attainment" or wisdom or spiritual power, but these notions end up being the misunderstanding of the ego.
Perhaps, to some degree, more libido is "freed up." But this doesn't have a distinct impact on the individual. The libido was there the whole time driving the individual toward the goal. With the achievement of the goal, this obsessive coniunctio-libido is actually depotentiated. Libido can then flow through that newly opened perspective "more freely", but with a lot less force behind it. That is, it's a movement toward equilibrium. The "tension of the Opposites" can generate an enormous amount of obsessive, directed energy . . . but the individuant must finally accept that the only way to achieve the goal (create the lapis) is to accept a depotentiation of the numinousness that the obsessive tension of the task generated.
But this is usually experienced as a big exhale, I think, followed by a quiet satisfaction . . . and perhaps even a sense of humor about how relatively small the goal turned out to be compared to how largely it was imagined. Still, some people thrive on the energy of Opposites. Artists, for instance. Many artists don't want to be "healed" or have their tension "depotentiated". They think (not incorrectly) that this will be a "loss of the Muse". Better to live in maya . . . that's the artist's credo.
