The term daemon speak of a non corporal entity tied to an element or concept. Those include:
-Discord who in a stroke of genius tied himself to Chaos.
-The timberwolves who tied themselves to dead wood and are driven mad by the rotting of their chosen flesh.
-Djinn who entered vessel in the possession of someone and are therefore bound to grant wishes to the possessor until the vessel is destroyed.
-Homonculus who are summoned for a long period so are given material to craft a body.

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Just seen the promo of the next MLP:EG. Here is my theory. Everfree forest on the equestrian side has a theluric sink hole that suck a bit of magic out of Equestria. Resulting in a more earth like ecosystem. Throw in some chaos magic gorged plunder vines and you got a spooky forest (note that it got a bit less spooky since the vine removal) . Now on the human side of things you got a leak of tainted magic (explaining why the sirens didn't try and consume it) that created a mad forest spirit.