Ooze

Don't touch that!
... And why were about to touch it, anyway? Yuck.
Yeah, it was moving, of course it was moving. That is no reason to touch it and, how else did you expect them to go from one place to another? Not everything in this world can magically teleport from one place to another like the Witnesses.
Yes, that is an animal. No, not a colony of microorganisms or what's left of something that used to be alive. It is a perfecly normal Ooze. They are nervous, lovely little creatures that feed on beuty and immediately produce a chemical that makes people either creative or sleepy depending on how was their day, makes other ghosts healthy or as kind as they nature allows, and triggers the formation of friendly beings and useful objects.
I heard people in the City of the lost tries to lure them with beautiful decoration, music, or gardens, whenever they are tired (or emotionally drained) but can't sleep well or for enough time, or when they have issues to design some solution at their jobs.
It's a pity that they are so scared of everything and everyone that they feel the need to attack anything that touches them. One would say that they would have enough with being able to seep through anything and having a body impossible to punch, stab or cut. But no! They also have the nasty habit of infiltrating your body if they feel threatened, and that can be really dangerous.
So, as I just said, don't touch it. If you want to flirt with death or touch ugly things there are plenty of ways of doing so without tormenting an already scared little animal.

Origin

It's very sad... but then again, there is sadness in the mere existence of Shards, and at least they get the chance to have and give some peace, right?
The Ooze ghosts are formed when any fear related shards mix with the pieces of the lost hope of peace and happiness of people whose trust was betrayed but pilars in their life. Many think that those shards are somehow related to the ones that create some Innocences, but there is only a small area of losses where those converge.
We can't tell for sure what triggers this ghost, and some biologists believe that just the contact between the right shards it's enough, but it seems that they are more common in places visited (or inhabited) by outsiders and clients.