These are beings of high power but they are basically humans that won't age or die due to natural causes that were gifted with immortality, and perhaps more powers by an S-Class monster.
What Are They?[]
A Child Named Jeff: The Documentary is the first Main Stream documentary that has discussed the topic, and showed how some people may be driven insane by mearly meeting the M responsible for granting an immunity to age, allowing the granted to grow to the age of 21, otherwise stopping it at the current age, and death of any natural cause. This Documentary Discusses the most Famous of the Immortal Serial Killers, Jeff the Killer. It also brings up Tiki Toby and Smiling Jack, two other Immortal serial killers. Fictional accounts and information that has come up has created a myth surrounding these ageless humans, and sadly that information has been added too.
The Immortal Serial Killers[]
To put it very simply the Immortal Serial Killers are Serial Killers who have been granted Immunity from aging and a natural death, and must instead be murdered. Their experiences may have cracked their mind, or the person's mind might become corrupted, as is the case of Jeff the Killer. In the Case of Tiki Toby, it broke Toby's mind clean in half. Sometimes they might also be granted powers, such as the fictional Walker (unidentifiable on videotape) in the only archived Clear Lakes 44 show.
Creatures of Shadow[]
A Creature of Shadow is normal person who has been granted the same immunity Immortal Serial Killers have. The Creatures of Shadow are often Allies of Hunters and are enemies of the Immortal Serial Killers.
A Child Named Jeff[]
This was a doccumantary on Jeff the Killer, as he was known, It wasn't very good as it brought up many useless "facts" about other monsters that weren't very factual. These include using "Fan-Fictions" that romantacized them, and memes that have nothing to do with the monster. It uses footage from cosplayer, Baptism on Fire as real footage, and Behind the Meme as its main source of knowledge. Amongst that it also exploited a young girl who believed Unicorns were her instigater that turned her into an Immortal Serial Killer. Unicorns do not exist, and if they did, their presence would not be a cause for a split or corruption of the personality.
How to Kill[]
In the case of Creatures of Shadow, as one might imagine, you must have the permission of the person in order to kill them. Immortal Serial Killers are merely humans, so anything that would be fatal to us, can be fatal to them, If nothing else shoot a shotgun slug at them and be done with it.