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... Isn't that the supposed definition of a ghost?
[ uh-huh, totally normal phenomena his butt. In his world, those people are called "akuma" and the fact they must be destroyed to save them, angers Bak like no other! (besides Komui, of course). ]
And they're your general creature gone awry. The giant wasps, in particular, are worth a mention. They can cause hallucinations and euphoria. It's a rather disturbing mix.