Youth vulture

Once upon a time, when the forest wasn't a forest and the premises where part of it, there was a traveling circus.
Everybody wanted to be their audience, for different reasons each, and there was nothing odd in that. Every so often, someone would want to be part of the show instead, and that was... well, people would usually laugh at them, because the circus people was clearly nothing like them. They could do things nobody in the world could. Fly. Sing impossibly low or dangerously high. Turn rocks into dust in their fists, or made beautiful sculptures out of nothing but ordinary dust. Cling to the surface or float away. Listen to thoughts or think aloud. Swim.
You are seeing the point already, aren't you?
Little Silvyath didn't see it though. She saw the impossible being done before her eyes twice a day everyday of a week, each time more evident that her friends were right to laugh and her parents were right to worry: the circus people were something from other world and she was just a random girl with little to no skills. But she didn't need to be special like them, she just wanted to be around. Be helpful perhaps.
And they took her in.
First they gave her a few rules: don't invade other people's tents, don't enter a town before it has been inspected by Scout, and other easy and inconsequential things.
Then they asked about her favorite meals, allergies and fears. How long she usually slept and how often she bathed. Some of the questions were actually a tad strange, but she was to happy about joining the circus to worry about that. 
She didn't mean to be part of the show, and was prepared to help with some trick or clean for them or something on those lines. But they said she would be a great dog tamer. That made little sense to her, as one or two of you might probably imagine. But the other said there were plenty of places where people liked to laugh with fun tricks of cute things. She was introduced to the circus dogs: small, cute and very sweet.
During the next days the circus was in town, she would take the dogs for walks at her favorite park, feed them, and teach them to shake. It was all fun even as she said goodbye to her family to travel to the next town.
The travel was strange. They took a common road, but after a while it was different of what she remembered, and instead of the neighbor town, it led to a huge city right next to the sea.
Because she was young and inexperienced, they told them a bit about how the prepared the tents and scenarios, but she didn't need to help with that for now, so she didn't really need to stay. She was a little bored as she waited, so she take her dogs for a walk. 
She didn't  feel any unexplainable worry when she saw the guy walking towards her by the same sidewalk.  There was nothing off about them, despite the strange outfit. No evil grin or weird demeanor. Her dogs didn't bark at him. Silvyath's neck hair didn't stood, and no little voice warn her about what was about to occur.
It was the man who noticed first. "Are those real beasts?" he tried to ask, right before the dogs jumped after him. He tried to run. She tried to calm the little creatures down. People yelled and called for law enforcement, but they only order everyone to seek for shelter.
It was the Scout who dragged the girl away from the carnage, and it was him who order her to take the dogs back to the area where the rest of the group was waiting for him. Where she should have been waiting too.
"There isn't enough of them to save," he sigh. "We must leave. Don't be too hard on yourself, it's hard to keep rules in mind at first. But I know you won't forget that we don't approach the city before me checking what kind of people they are, what could they do and how they could be hurt."
That night, she finally asked the right questions, and the other entertainers where surprised to find out that all this time she hasn't believed their name: The Otherworldly Circus was exactly that. All their mystic vibe was in truth, cultural shock.
What's ordinary tech for you looks impossible to me. A natural skill of mine is impossible to you. Every single one of them had once been normal people in their own world. Except the Scout, perhaps. He fit everywhere and belong to no place. Like the witches and genies, like every wish Granter... or so the story says.
And the path they took to go from town to town, a different world each time, was... this. Our world, ages ago. And despite the looks it was the same it is: the home of the shards, where they can sleep or mourn or rest or... be ghosts.
When they came back to the path, our young heroine still crying and fighting for her sanity, the shards of the life she had ended by accident mixed with the shards of the affection and trust she had once have for the circus dogs. They were influenced by something in her. Maybe the hope for it to be a dream, maybe her guilt and the impossible dream to take it all back.
Something resembling a person, not dead, not alive, a body and a mind, but no soul and no energy started walking next to her. It fed on her physical strength and will to live, making her too exhausted to be scared.
The Scout noticed it was too much effort for the girl, and forced the ghost to leave. Some say he didn't care that it would starve. Some think he knew the creature would find humans lost in this world. The truth is, whether he knew it or not, this kind of ghost don't starve.
They stop.
You will see them from afar once in a while: very realistic statues of sleeping people in caves or improvised shelters in the forest; or even worse, lying in the path or next to it, as if they had been trying to arrive to a safe place.
Don't go near them if they are too many, or if you are in poor health of body or mind. You see, they need little energy each, and they are usually decent enough to not wanting to kill you, so you should be okay if you are more alive that they are dead. You see, the youth vultures only want to be alive, and usually they care a lot about other people wanting the same—which is probably why a biologist decided to name them after scavengers instead of predators. But they don't know if they are taking too much, and not all of them will stop feeding on you because you say you are feeling dizzy.
A Beat will prevent them from taking all of your energy, but the encounter will debilitate you nonetheless, so you will still feel exhausted and sick if you approach more than you can feed. It might even be bad enough to trigger another condition in your body and killing you on the long term.
If you feel confident—or suicidal—they will be thankful for your help. They might want to pay back, or be easily persuaded to do so, but honestly, you need to be quite a monster to ask to be paid for providing food to a starving being, even if said being is a ghost.