The similarities between the currently depicted demons as they move to posses folk, hide in the this unfortunate fellow's chest, and other recent scenes have me convinced that they are a similar type of being to the anima creatures that we saw in the related dimension / story arch. Such as the arch of demons linked behind the fellow looks strikingly similar to Dr. Slock's anima.

Is there a chance the way they left that place caused the current demons issue?
Is this just an echo of that other dimension with no actual relation?
The shape of the Ferryman looks to me like a modified soul... to look like a boat. Also watch those tentacles, remember who the party left back in that dimension?