Some years ago I used to be haunted by a spirit who followed me around my house. It never left the house and never went outside, but as long as I was inside it was there. I could vaguely see it during the day, and saw it much more clearly at night. It was made of the specks of color that one sees in low lighting, that grainy look; it was as if these were much more concentrated where it was and I can assume that is why it was easier to see in the dark. It basically looked like a dark spot during the day, but I could make out color at night. It always sat like a frog, and when it walked it crawled on the ground like a baby, though I rarely saw it move, it usually was just there, sitting there. It always watched me, staring at me, and slightly bobbed its head, but did nothing. I had my bed on the floor at this point in time, and it would sit beside my bed and stare at me. I was very frightened of it at the time, and tried wishing it away many times, and prayed for protection or for it to go away, but it never did. I could never see it clearly, however occasionally I saw its face in the mirror. It's reflection, unlike when I looked at it, was clear. It only ever let me look at it for a second or so, but what I saw was rather horrifying... some kind of creature with the widest smile you've ever seen, gigantic eyes, and, well, when I describe it it just sounds silly, but it looked very ugly and unnatural. It had a wild mane of red hair and olive-green skin. I only occasionally saw it in the mirror, however, and it usually stuck to being vaguely visible.
Well, eventually I figured out that praying for it to go away or telling it to wasn't working, and so I simply thought to myself that I needed to learn to deal with it. It wasn't harming me, after all. And so, I started ignoring it. I soon stopped fearing it, and just lived as though it wasn't there. After about a year of that, it went away, and I have never seen it since. It has been three years now. The duration of time it had been around was four years.
I know it sounds kind of crazy - I've never heard of a spirit being so forthcoming with its appearance like that. I can guarruntee you I have no mental illnesses and what I experienced wasn't fake. Someone I know once told me that perhaps it was a good spirit, because looks aren't everything. However, I always felt very strong negative energy around it; actually, a feeling that told me "Run!" Sometimes I would feel this energy and then turn around to find it there. However, it could have been my own fear of it that was projecting that feeling.
For some reason it popped into my head recently, and I am wondering if it is possible for a good spirit to look frightening. I've heard of spirit guides and the way it just sort of hung around and followed me sort of reminded me of that, and someone I know thought that maybe it was guarding me rather than trying to scare me.
I never had any other occurrences associated with paranormal while it was around. I could have sworn it touched me once, and at a point I felt someone blow on my neck when no one was there, but other than that, none of the traditional stuff I've heard about with ghost stories or similar supernatural tales, but then again what I know is limited.
Is that possible? Could it have been good? What do you make of the spirit?

The world is full of mysteries and things we cannot explain or understand .
Since your "spirit" seems not to fit a traditional mold at first glance here is an extremely nontraditional theory that is gaining some followers.

A new theory is that we are composed of "vibrating strings" that are the elementary particles and building blocks of the universe.
All strings (matter) vibrate at varying rates.
And other parts of the universe that vibrate at a rate close to yours will be more "in tune" with your reality, and you with theirs , giving you a symbiosis of sorts .

So in this light it could be an interdimensional phenomena that is thought by some to explain ghosts and spirits.
But if it is good or bad can only be determined by action and effect in this case.

This is as far from traditional as it gets at the moment , but what wonders has God given us to ponder?

String (physics) - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/String_(physics))

Martini is right, this world (including that spiritual plane) is full of things that can just be beyond us. A famous evangelist got to know a VERY powerful witch doctor for some time and there are things he said that would just make your head spin. There are truths in the spirit world that we cannot understand and really don't relate/apply to us. Why they (spirits) look the way they do is something we are not going to be sure of. They can make different manifestations seemingly at will. I strongly urge you to rest assured with your gut instinct to know this thing should not have been trusted. While the "looks can be deceiving" theory applies great to humanity, I do not believe this is something we should use for the spirit world. I believe the only good looking glass to view the spiritual world through is the Bible. This thing you used to see fits very well into the "bad spirit" category. While it's intentions and long term effects may not be obvious, the Devil (and his angels) can always be expected to act in deceit. I'm glad, for your sake that it appears to be gone.