Merdoons corner of riddles.

"In one of the darkest corners of the lab you find an old tome. The dust on the cover is so gnudeg in that i can baerly be removed. On the cover it is writen with old tadered letters: Merdoons book of riddles. Curiously you open the tome and a dark mist covers everything around you. You wake up in a room with only a door behind you and a well of inc in the middle. Placed on the side of the well is a old quill. The rooms walls, floor and roof is covered with riddles. You glance trough the door and you see yourself sitting on the laboratory floor with your face deeply burried in the book. You start to read some of the riddles that is scribled over the walls and feel an ebrase to write some of your own thoughts down. Hours have past since you first enterd and now you leave, only to find that it has mearly been a couple of minutes. you place the book back on the table and leave it be... for a while"
(( Basicly you can write down your own riddles and try to answer old ones to, here i will write the first one))

I come from the dark never seen never heard.
You can never see me but every one else can.
I change everything for you but never for no one else.
I steal the thing the most dearest to you and dwell in its place.
You live with me until you die or die by my hand.

What am i?

((Feel free to corect any of my speling mistaces. I am not a wery good speller ))