A few notes. I think you're design is short on the "dark" part of darkade. I think a few parts of the design undersell the dark theme. As another poster mentioned; Scooby. Right now this art suggests saturday morning cartoon scary, unfortunately, not in a way that is clever or intended. It's a watered down version of "dark" a Nancy Drew primer on the subject, but not truly dark.
I have a few suggestions to increase the intensity of the image, without altering the overall theme.
1. Pick a new font that isn't a "script" font. This font suggests "Black Beauty" or some other campy 70's story. Script fonts rarely provide any good design. It takes a very talented designer to use a script font in a clever / interesting way, and this use of it does not enhance your theme.
2. Dont' ues the swirl. Right now it is a distraction from the overall imagery. Less is more. The wispy swirl just lessens the impact of "dark." It adds "camp" to the image... not in a good way.
3. The use of the purple fades at the bottom is very arbitrary. Why is it there? It currently is doing nothing, other than acting as a purple foof on top of a blue field. My only guess is that it is there to break up the blue field. I don't think it is working in its current form... it's just a distraction. Use the color judiciously to add intensity to the overall image.. to enhance your theme. Right now it is just not working. I don't have any concrete suggestions, other than to suggest that the purple needs purpose.
4. I would suggest making the pattern in the background more graphic. Get rid of the cheesy emboss effect, simply use color to define the pattern. I would also suggest making the pattern much more faint in its current form, the abstractness of it will give it greater impact OR use a pattern of runes instead, ones that connote ancient secrets, magic, lore... that kind of thing. If the current pattern is based on something, I can't discern what it is.. it just feels like wallpaper. The repitition is too obvious, and that needs to be toned down.
5. The face in the background. Dump the left eye, or make it more graphic. Eyes are windows to the soul...the larger they are, the better we can see to the soul. There is a reason a lot of bad guys in movies and comics have weird eyes. It's unsettling. The left eye currently does not carry enough menace.
6. If you are going to use something to set the edges to black, I would not suggest a fade. Create something to view the imagery through. Make the black outline look like a whole in an ancient, large blocked brick wall. Your imagery is already cliche, you might as well just dive fully into the cliche and explore it. A fade will suggest lack of interest in designing this fully, lack of thought. Explore the theme of how the cabinet art should connect to he cabinet.
When I initially looked at this, I reserved my comments. I did not want to poison the well with my first impressions. I DO think you have some good elements to work with and some good ideas. Intense eyes, cool / spooky castly elements.. I like the idea of a castle just as the sun goes down, which you've started to capture. The time absolutely furthest from the next day. That's good stuff. However, using graphic elements set against patterns and semi-photographic imagery is a rather ambitious start to your side art. Right now this has too many cliched visual elements thrown together with a hodge-podge of photoshop effects. Overall, I guess I can sum up my comments with; If you are going for cliche / camp, go ALL the way. If not, sit and think about what DARK is, do some reasearch, take a look at some of the great artists work on the subject, look through the horror section of a bookseller, rent a few of the stranger movies about darkness (the Wicker Man, for instance)
All of that being said, please note, I think what you've attempted here is much more different / difficult than most of the subjects / themes usually posted & discussed here, and I give you props for that. Part of my job is to be very critical; especially when people ask for it. Please don't take this