Diverting the River Styx.
This was an extremely dangerous act.
Because at any time, whoever dared to tamper with the River Styx would be considered by the death pantheon to be committing a very serious act of provocation. This could even lead to a God's Realm War, so even when the Time of Troubles broke out, practically no one dared to meddle with the River Styx. This situation persisted until the disappearance of the Lord of the Dead, Kelemvor. With the God of Death, Naram, and Kelemvor at odds, some audacious individuals finally began to harbor ideas about the River Styx.
Without a doubt.
Soren was one of those audacious individuals!
The greatest value of the River Styx itself was transportation. Yugoloths and some fiends made a living by ferrying across the River Styx, and they also served as assistants to the death pantheon. However, the truly most valuable thing about the River Styx was the cargo it transported—namely, souls from all over the multiverse. Regardless of race or plane, the vast majority of souls had a connection to the River Styx.
Soren's target was the Realm of the Forgottens on the third floor of the The Abyss.
The Realm of the Forgottens had been mentioned earlier, but one point had to be reiterated here: the birth of the name [Realm of the Forgottens] was closely related to the River Styx itself.
In this layer of The Abyss, many demons found it much easier to forget certain things than in other places. Even people from other worlds who arrived here had to pass through a mandatory saving throw after staying for a period of time, otherwise they would lose certain past memories. The forgotten memories were related to their own abilities and the importance of those memories.
What they forgot