Thread:ElsaRules!!!/@comment-28082245-20170101023549/@comment-5782071-20170204014235

Please be warned, Esla, this has a lot of spoilers.

Hollows are Peculiars that were transformed by a terrible experiment in an attempt to make themselves immortal, since Peculiars hide in Time Loops that restart one single day over and over. Thing is, once you're in, and then you go out, you instantly age as long as you were gone after a few hours (one Peculiar aged from a child to an old woman). The evil Peculiars, who wanted to rule the world, wanted a way to survive without Loops. Long story short, they were instead turned into Hollows, which Ms. Peregrine, the Ymbryne time manipulator, theorizes to be because they were were de-aged to a time before even their souls were conceived.

Hollows are sorta like Slenderman in that they're tall and pale with featureless faces except for a large mouth with lots of teeth, and multiple long and strong tentacle tongues, and black blood. Hollows that consume enough Peculiars (in the film, this was changed to merely the eyes of Peculiar children based entirely off of one offhand comment in the final book). With enough consumption they become Wights. They, I think, are Soul-less beings? They have their original form, but lack irises and pupils and, contrary to the film, lack powers (except if they harness the souls of other Peculiars after extracting them, which also lets them enter Loops, which they are otherwise unable to do).

Jacob and his father are Peculiars with the ability to, I think, sense and see souls, seen in the final book as Jacob could see the Peculiar souls in the Library of Souls. Through that ability, for some reason unexplained other than "that's what you needed your ability most for, so that's how you trained and developed it", he can see and after prolonged time with Hollows, even control them with immense talent.

As for reanimating the dead, Enoch, the child who can do that does so by taking the hearts of other living beings and implanting them in other bodies, or objects (at the very least, objects that represent or resemble something real, like toy soldiers). In the context of reviving humans, it relies on the fact that there is an Afterlife in the books' universe, as evidenced when he brings back the deceased child Victor to talk to him on occassion, who says that he likes where he is and does not wish to come back to life permanently. However, he is limited in that depending on the size and/or complexity (can't remember, likely the former), the heart must be strong enough to sustain the thing is is reviving. I believe humans could be the hardest, but I'm not sure. When a person is revived, they mostly long to go back to the afterlife, and do keep their memories, but I think also still feel pain (a man who was violently assaulted by a Hollow and was revived said he was in pain). I'm not sure what else there is but I think that's all the mechanics of it.