Hundreds of millions of years after Creation, there was a world without life nor death. Only humans and souls existed together in a single realm of existence within a self-contained cycle. Eventually, hollows came into existence, disrupting the cycle by devouring souls. Inevitably, the first menos soon came into being too, slowing the cycle of souls, and ultimately leading to a future where all souls would be eventually consumed into one menos. But almost in response to its existence, the Soul King was born. The Soul King vanquished the menos, and the self-contained cycle of souls continued once more. Unfortunately, the world eventually fell back into chaos as the Soul King continued to vanquish hollows. Soon after, 5 ancestral heads of the once 5 great noble families gathered. They intended to pool their ideas to serve a shared vision of changing the state of the world. The Tsunayashiro ancestor was afraid the power of the Soul King would one day be used against them. An unknown rival family ancestor wanted to cover up the 'pit of chaos' that would become Hell. The Kuchiki ancestor wanted to implement a new world order to bring balance to to the world. The Shihôin ancestor wanted to widen the cycle of re-incarnation to avoid stagnation of their world. The Shiba ancestor wanted to create a method to purify hollows, reverting them back into souls. (They recognised that hollows had lost hearts that were worth saving.) And so, a shared goal was born to separate the World of the Living from the dead. At the Tsunayashiro ancestor's insistence, the Soul King was bound and sealed within a crystal.
The Soul King's power of The Almighty served as the keystone to separate and maintain the 3 worlds. The World of the Living for humans, Soul Society for the souls, and Hueco Mundo for the hollows.

Then the Soul King, who most likely was bored out of his mind of being inside that crystal, created a little baby. The baby back then couldn't see, hear, talk or even feel, but he had a power, whatever feeling or damage a person had, if they touched the baby it was cured, so if the person had depression that's cured, or had a heart attack that's cured, however a few days later the person dies and it all that power granted to them went back to the baby. As that continued and went on, the baby was finally able to hear and his name got to be known as Yhwach Bach. Yhwach learned about the Soul King's existence, later on in his life time, and wanted to return everything back to how it all was, back to that one universe, so he needed an army to do it all, that came the birth of the Quincies. And holy crap, Yhwach is broken in just his base state, he stole Yamamoto's Bankai (its implied you need to be relative to the captain in ap to steal the Bankai), a weaker variant bodied Kenpachi who defeated a being as strong as Vasto Lorde Ichigo, who can destroy Hell, a multi planet level place, and this is all him in just his base state.

Being the God of the Quincy, Yhwach fights by absorbing Reishi around him and makes weapons out of it.

This includes things like bows and arrows, a sword, giant bows, etc., and all of those attacks erase the existence of a soul.

However he can do more than use bows and arrows, he has other techniques to help him:

Sankt Altar: Allows Yhwach to take away hax and abilities... although we barely got to see him use it.

Sklav Rae: Allows Yhwach to enslave Reishi, he can even absorb Hollows despite the fact that Hollows are poisonous to Quincies.

Blut Vein: A defensive technique that amps Yhwach's defenses drastically, by focusing his spiritual pressure onto his veins, and he can extend his Blue Vein to make a shield and take over someone's body, both of which he did with Ichibei.

Blut Artery: Its the offensive variation of Blut.

The main flaw with Blut Vein and Artery is that you can't use both at the same time.

Hirenkyaku: A Quincy's high speed movement technique, it is a far more efficient technique than shunpo in terms of spiritual-energy consumption. There is even a technique that allows you to make a Reishi foot hold and use it as a platform.

Sankt Zwinger: The ultimate Quincy offensive and defensive technique, these pillars of light appear to protect the user and if you step on the light, you get eradicated.

Now its time for the fun part of Yhwach, his main Schrift, the Almighty: The Almighty is the ability for Yhwach to SEE THE FUTURE! And not just one future, he can see ALL futures and can pick and choose which future best suits him, so if he is going to lose a battle he can just a pick future where he wins. Like how when Ichigo first shown his True Bankai, Yhwach broke it by choosing a future where it is broken.

The ability is also a passive hax, as Yhwach can even use it WHEN HE IS DEAD AND REVIVE HIMSELF WITH IT!!!!!!!

He can even negate attacks on a conceptual level, coming from the fact that Ichibei can control manipulate the names of things on a conceptual level, he changed Yhwach's name to a Black Ant yet Yhwach was like "Almighty gg".

This feat was performed when the Almighty was fodder. All it did was view the future and negate abilities.

Yhwach also absorbed the Mimihagi and the Soul King, so he does also have some of their abilities, like with the Mimihagi he did those little clones, manipulates shadows (whatever those are) and gain accausality type 2, Characters with this type of Acausality do not exist in either the past or the future, only the present. This means they cannot be affected by changes to the past, while also making them resistant to Precognition that works by viewing the future, as they do not exist within it, and Fate Manipulation, for the same reason. In essence, they are able to choose their own fates, but they remain just as vulnerable at the point in time in which they do exist.

https://youtu.be/mfOdv2hiroI

Now for his ap and speed. Yhwach's ap is multi solar system, because he was going to merge all the dimensions in Bleach, Soul Society, World of the Living and Hueco Mundo, all of them contain multiple stars.

And yes they are separate dimensions because just the Soul Society and the World of the Living are separated by their space time, because the Dangai is what links them yet its a cut away of their space and time.

And as we know, Yhwach was going to merge with raw power. As for speed, Yhwach should be light speed, characters who are fodder to him dodged light, Ichigo blocked a Cero which is light speed,

Lieutenants dodged the Neggaccion light,

Aaironeiro dodged light with his back turned,

Toshiro in Shikai dodged Shinso which had to be around 191 times light speed:

Shinso is 10 pixels away from Toshiro's eye, or about 1.10577 mm away or 0.00110577 m. Shinso travels at the speed of light.

To find the time frame, the formula is T=D/S.

Now the time frame:

0.00110577 meters/299 792 458 m/s=0.000000000003688 seconds.

Now Toshiro moved at 90 pixels or at 212.1 mm or at 0.2121 m as in on the panel.

Now to find the speed, we can use the formula of S=D/T.

Toshiro's speed is:

0.2121 meters/0.000000000003688 seconds=128 648 098 575 mph or 207 039 045 553 km/h or 191.8355 times the light speed.

And for course, this is Toshiro when he was fodder and Yhwach scales FAR above him. Now for stamina, Yhwach has more than 3 MONTHS worth of stamina, because Ichigo did mental training (that also took physical damage and it was more fighting) that lasted for 3 months, and Isshin also used his spiritual pressure for 3 months as well. Yhwach scales MASSIVELY above both of that Ichigo and Isshin. Yes you can measure stamina via how much spiritual energy quantity, because Ichigo before stated that based on how much spiritual energy he had he can measure how much stamina he has.

He is also smart, he can plan out a strategy, like when he distracted Yamamoto to fight Royd, so that Yhwach can talk to Aizen, but he kinda becomes arrogant when he obtains full power, and he also got defeated by plot induced stupidity. But overall, its no wonder Yhwach is seen as a broken villain.