Nicely done.
Not totally sure about the Harry Potter part of the characterisation, but I can really get the Mountain King idea of this. Definite Grieg vibes, throughout.
Not totally sure about the sound of the drum roll at 0:15, that could have standed to be a little more subtle. But that asides, the rest of the percussion in the 0:20-0:48 area and continuing further create an even more ominous feel accompanying the strings. Very nice stringwork, by the way; the melody is very clear, but haunting at the same time, and you use the pizzicato to tremendous effect.
The acceleration reminded me a lot of Grieg again, it was very well done. Melodically, the strings before 2:40 where the main tune comes in again were again, very haunting, but with an added tension to them, also.
The ending was also very good, I liked the abrupt silence before the final chord. Though the cello (I think) which bows the two notes at 3:40 doesn't seem quite right, sound-wise. Maybe because the dynamic of the instrument is negligible just before it, and then it just abruptly comes in with these two notes...I don't know why it isn't sitting right in my head, to be honest, which is a sure sign that I've just listened to the ending too many times.
Anyway: Evidently you've dived into Kontakt like a fish to water and it's achieved a very successful piece. I'd be interested to see what you'd accomplish once you know the software a little better. Excellent work.