Can you tell us a little more about what you’re looking for? "Dark" can mean "sad" or "scary" or "slow" or any number of other things. For instance, I don’t know if you’re looking for piano pieces with this (http://www.youtube.com/watch?v=TQRyhMhrWKU) kind of mood or this (http://www.youtube.com/watch?v=ezYp2qca3O4) kind of mood or this (http://www.youtube.com/watch?v=L4ZZXYH8JcI) kind of mood.
Also, are you looking for songs from any generation of consoles? Or only newer stuff?
If you’re looking for references then this song doesn’t have much to offer in the way of piano.. but when it does play it’s beautiful and dark.
YouTube – Jazz Jackrabbit 2 – Dark Groove (http://www.youtube.com/watch?v=7OR9esOvUUc)