(LORE) when ever a person kills another person this black stuff start's to grow on them and it can grow literally anywhere on they're body and i mean ANYWHERE its caused by the spirit when someone dies part of they're spirit stays on earth and usually gains otherworldly powers and chooses someone to inherent them but when someone is killed by another person the spirit instead latches on to them and leaves the black stuff you see in the image and the more people someone kills ether by accident or on purpose the bigger and bigger it gets and in extremely rare cases the black stuff can temporarily take control over the person who killed them and can do whatever besides getting revenge for some reason and if someone is being controled by the black stuff and kills someone it doesn't make the black stuff grow.

The only way of knowing if the black stuff is controlling someone is by they're eye color they're eyes always turn yellow when the stuff (im gonna start referring the black stuff as just stuff) is in control.

Besides all of that it's basically harmless and totally doesn't make the person who killed them have terrible nightmare's about warped and twisted versions of the people they killed and anyone they know trying to kill them.

and there's no known way of removing the stuff ether.