Unsouled

Near the start of act 3 you'll pass an archway with a soul focus prompt, instead of destroying it head up and through the doors to find the twisted soul which you'll be returning to soon. Further ahead you'll reach a puzzle section and at the end of it will find the soul of a child, after receiving the child's soul backtrack to the twisted soul for a scene.

This has to be done in the same attempt, returning in another run doesn't activate the twisted soul even though you have the child's soul.