On the Greysky theme- the divisis in the clarinet are a bit strange. I'd assume, given the minimalist score, that there would be one member of each instrument playing. However, three clarinetists playing to balance one bass would be a bit strange. As is, if I saw the part without any context, I'd guess piano to be the most appropriate instrument. Everything else is good, though. Schazzy bass line.
The Roy v. Thog thing is interesting. It's a strong departure from the tradition of percussion and brass representing battles, which I suppose is alright. You've managed the A, B, AB idea quite well, which is rarely easy. It's a good piece, but two warriors meeting on the field of battle is not the image that it conjures in my mind. The energy is there, it's simply manifested in a scotsman dancing a jig vs. a raging half-orc. Are you familiar with text painting?
I'd suggest changing the piece to add in the sounds of a battle. Arhythmic, percussive attacks, drums playing a heartbeat, that sort of thing.
All in all, good writing. Very impressive, considering that you've *only* been playing for half a decade or so.
Also, I can both compose (reasonably) and play (very well, if I do say so myself) piano. I can sort of play violin and horn, too.