Maverick figured out the purpose of the devotional statues in the end, but was a little confused at first. He figured he would share his findings here.
The Devotional Statues Lead to an Optional Miniboss
The Devotional Statues in Fellshrine Ruins are a new addition in 3.25, Settlers of Kalguur. They are a core feature, meaning this post is still relevant if you’re reading it during a later league. In other words, they are a permanent feature in all feature leagues as well (unless the devs decide to remove them at some point).
If you landed on this page, you likely already found a Devotional Statue. There are 3 Devotional Statues in total, so you’ll need to find and activate 2 more spread out over Fellshrine Ruins. Just look for Stairs going down on the Minimap to find them relatively easily.
Once you find and activate all 3 of them, head to the right of the area, in front of the area leading to the next area (the entrance to The Crypt). If you activated all 3 statues, the Forgotten Daughter will be waiting for you there.
This optional miniboss has elements of both Vorana and Xenathar (Floor 3 Boss) from The Forbidden Sanctum. She is a bit tougher than other minibosses at this point of the game, but will not take an incredibly long time to take down. Although she does not seem to have any guaranteed loot, she tends to drop quite a lot more than other minibosses, especially rare items.